Not for the first time in his career, Button made the right calls in a complicated wet race, and more importantly, he demonstrated that he understood how to be patient, and play the long game.
The numbers that day were extraordinary. Quite apart from his winning average speed of 46mph for a race that officially lasted for over four hours, Button pushed the boundaries by making six visits to the pits, including a drive-through and two slow crawls back to replace punctured tyres.
Indeed at one stage he'd made three pit visits – putting on intermediates and taking them off again, plus the drive-through – when many of those ahead on the road hadn't stopped at all.
In total he spent 2m21s of his race in the pitlane, compared with the 47s of fifth place finisher Vitaly Petrov, who made it home with just two stops. He also survived contact with Lewis Hamilton, Fernando Alonso and Pedro de la Rosa.
One of his laps, returning to the pits after the clash with Alonso's Ferrari, stretched out to 3m05s. Perhaps most astonishingly of all, from lap 37 to lap 40, he was classified 21st and last. And yet somehow, he still won the race...
"It's too much to take in," McLaren engineering boss Paddy Lowe told me as the celebrations kicked off. "I still can't compute that we won that race really, from the back!
"In fact we were so far at the back that they were about to pull the safety car in and we still hadn't caught up with the train. So we were worse than last..."
Here is the story of Button's extraordinary afternoon.
Sebastian Vettel and Red Bull were on top form in the early part of 2011, winning five of the first six races, and losing out only in China, to McLaren's Lewis Hamilton.
Vettel duly took pole for round seven in Canada, while running higher downforce with a view to a wet race, Hamilton and his teammate Button were only fifth and seventh.
Although the Sunday morning rain had stopped before the start there was still potential for spray, and four laps of safety car running allowed the drivers to drain a bit of the water before the field was released.
When the track went green Hamilton and Mark Webber tangled in front of Button, who gained a spot from the Aussie but lost one to Michael Schumacher, ending the first racing lap still in seventh.
On the next lap he gained another place when Hamilton ran wide. Lewis was keen to make amends, and when Button got the final chicane slightly wrong at the end of lap seven, he made an ambitious move up the inside of his team mate on the pit straight.
We'd seen the pair race to wheel several times in the past – notably in Turkey the previous year – without any dramas. This time, it didn't work out, and contact was made as Hamilton found himself edged towards the pit wall. Button insisted that he had only seen a flash of colour in his mirrors, thinking that it was his own rear wing.
"Both drivers understand what happened," McLaren team boss Martin Whitmarsh explained later. "Lewis was trying to overtake. Jenson didn't see him on the inside there, and it happened. I think Lewis has accepted that.
"It's very easy for drivers to get irrational and start blaming team mates and all those things, but I think the spirit between the drivers is robust enough that it can withstand that sort of incident…"
Hamilton's right rear wheel rim was shattered, and the tyre was flopping loose. His engineer told him to park the car, cutting suspension damage and possible consequences for the gearbox.
Alighting from the cockpit Lewis made a point of looking over the front and rear suspension – he even gave it a kick! He was clearly frustrated at being told to abandon what he thought was a repairable car. However given the broken wheel the likelihood was that the FIA would have ordered him to stop on track anyway.
Whitmarsh had no regrets: "Had he managed to get back, and bear in mind the rim was completely shattered, then that would have fallen off somewhere, which could have been dangerous.
"It probably would have ended up damaging the floor, and even if it hadn't, and he had to have a front wing change as well, he would have been one lap down.
"You can debate should we have battled on? But we are responsible for the safety of the drivers, we've got to take a responsible decision, that was a bit of a knee-jerk reaction for safety."
Button meanwhile had a left rear puncture from the incident, and he had to crawl back to the pits for a replacement tyre.
In an attempt to salvage opportunity from disaster, McLaren put Button onto inters. The stop demonstrated how pitting under the safety car in Montreal is less costly than elsewhere, for while he crossed the start/finish line at the end of the pitlane in 14th, by the time he'd charged out into the pack at the first corner complex, he blended into 12th place!
The safety car made the tyre choice a little less risky in that there were for laps of slow running, which helped the track to dry further. Unfortunately during the yellow period Button exceeded the speed limit, and that earned him a penalty.
"Jenson got a drive through for not meeting the safety car timing," said Lowe. "He was a little bit too quick in one sector. In trying to make up the time he overcooked it."
He couldn't take the drive-through under the safety car, and thus came in at the first opportunity after the green.
After serving his drive through Button was in 15th place when he crossed the line at the pit exit, and by the end of the lap he had gained a spot from Sebastien Buemi. The lap after that he passed Pastor Maldonado and Adrian Sutil, and he gained a further spot when Rubens Barrichello pitted.
There was a brief window when inters looked like an inspired choice and Button's pace encouraged others to stop, including Fernando Alonso and Mercedes drivers Schumacher and Nico Rosberg. However, even as those guys were pitting, rain was coming down again.
During this sequence Button rose as high as eighth on lap 18 – but his race was about to go badly wrong, and he wouldn't reach such dizzy heights again until lap 50.
"He was the first car to go for inters," said Lowe. "A few others then followed suit. It proved to be a bad plan, and we had to go back onto the wets..."
As the rain intensified those on intermediates knew they were in serious trouble, and began to change back to wets. Button came on lap 19 just as the conditions caused the safety car to be dispatched again.
Button dropped three places to 11th as he joined the safety car queue, soon gaining another one when Schumacher pitted for wets. After a few more fruitless laps, with the rain really coming down, the red flag came out, and a lengthy wait ensued.
The frustration for Buton son was that had he known a red flag was coming he could have stayed out on the inters and changed on the grid. So as in Monaco, where his chase of the leaders was spoiled by a free tyre change for all, that rule didn't work in his favour...
During the break Button found time for a discussion with Hamilton, and clearing the air over their collision could only have been good for his state of mind.
Meanwhile the team had time to question the wisdom of the early switch to inters – and the bad luck of going back to wets just as the safety car came out.
"There were plenty of regrets while we sat and watched during the race suspension!," said Lowe. "We were thinking, why did we do that? There was a safety car, we put the wets back on, and then they red flagged it. So actually we ended up in P10 and we could have been P6 and got a free tyre change."
"You can do a lot of examination and soul searching of what happened, what might have happened, what you should have done before," said Whitmarsh. "But actually you've got to focus on the fact that there's a race on here, we've stopped for a long time and we had an hour and 14 minutes left. We knew a lot could happen, and of course it certainly did..."
Button had a new set of wets for the resumption, while others stuck with a used set. After nine laps behind the safety car the field was finally released at the end of lap 34. At the restart Button got ahead of de la Rosa, who then tapped the rear of McLaren and lost his Sauber's front wing. This time luck was on Button's side, and he escaped without damage.
Several cars at the tail of the field went straight into the pits for inters at the restart, and Button came in at the end of the first racing lap, as did Nick Heidfeld and Paul Di Resta up ahead.
McLaren refitted the scrubbed intermediates that Button had used earlier in the race. The stop dropped him down to 15th, but with others pouring into the pits he soon bounced back to 11th. Alonso had pitted a lap later, and came out just in front. Button's tyres were up to temperature and he was already dialled in, so he immediately took a run at the Ferrari – contact was made, and the Spaniard spun off.
"Jenson was up on the inside there," said Whitmarsh. "Fernando may not have seen him, but I think he probably knew. If you turn in and don't give someone the space on the inside, you're going to have an accident…"
Once again Button continued, albeit with a puncture. He faced another long run back to the pits, where he collected a set of fresh intermediates. With Alonso's Ferrari stranded on the kerbs the safety car emerged again, so that limited the time lost.
Button was now 21st and literally last. He also had to catch the back of the safety car queue, something he didn't quite manage – when the green flag flew at the end of lap 40, he crossed the line still some 2.4s shy of Tonio Liuzzi's HRT, instead of being on his tail.
"Jenson came out in last place," said Lowe. "But they decided to pull the safety car in when he hadn't yet formed up. Probably the rationale for that is when somebody's had a pit stop, they ignore them, and don't give them that chance to catch up.
"So he was having to drive absolutely flat out to try and catch up with the train, and he was still a few seconds off when the race went green."
On the plus side he'd run a couple of very fast laps catching up, so he was in the groove at the restart, and was soon weaving through the backmarkers.
He soon passed Liuzzi and then over the next few laps took Narain Karthikeyan, Jarno Trulli, Jerome D'Ambrosio, Timo Glock, de la Rosa and Buemi.
Stops for di Resta and Sutil gifted him a couple more places, leaving him in 12th by lap 45. After holding station for a while on lap 49 he passed both Maldonado and Jaime Alguersuari.
Now the window for slicks was beginning to open. Webber and Barrichello were the first of the cars ahead of Button to stop, coming in on lap 50, before he was called in a lap later.
The team had already earmarked lap 51, and encouraged by Webber's quick sector times, Button duly pitted, slipping briefly from eighth back to 10th. He only had used supersofts left, while of the frontrunners only Schumacher had the advantage of a new set.
"We could have gone a lap earlier, like Webber did," said Lowe. "Webber picked the right lap, and we were kicking ourselves at the time for not doing that. We had planned the lap we actually did, and Webber jumped the gun on what we thought was quite an aggressive early move, and he went every more aggressive than what we'd be thinking.
"We only had to watch and immediately we saw he was setting green sector times. That confirmed our plan to bring Jenson in. What was surprising was that no one else came in at that point. Vettel left it another two laps, and that was curious."
As others stopped Jenson soon began to climb the order again, helped by the fact that on slicks, he suddenly seemed to find an extra gear that no one else had.
"For whatever reason, our car worked well in those conditions," said Lowe. "For most of the time on the slick tyres we were two seconds a lap quicker than everyone in the field, which must have given Red Bull a bit of a shock."
Everyone else stopped within a couple of laps of Jenson, but they were too late – he had charged up to fifth. In other words over the course of the mass switch to dries he had gained five places, getting ahead of Barrichello, Rosberg, Petrov, Heidfeld and Felipe Massa (who crashed).
Kamui Kobayashi was struggling on slicks, and Button soon dispatched him. Thus as of lap 55 the order looked like this:
So, with 15 laps to go Button was 15 seconds behind the leader – and on that lap 55 alone he had taken an astonishing four seconds out of Vettel, who was still finding his feet on slicks.
The next lap Button sliced off another two seconds off Vettel, while also catching the Schumacher/Webber battle. This was getting interesting...
Then we had another safety car interlude triggered by a crash for Heidfeld crash. Although he was already on schedule to catch Vettel it made Button's life even easier, as all those gaps shrunk to nothing. However, he had D'Ambrosio's lapped Virgin between himself and Webber.
"In the end the shame I guess for Sebastian was that there kept being these safety cars, which would erode his advantage," said Lowe. "He kept building up these massive leads, which kept being knocked back."
After three laps of yellow the field was released at the end of lap 60, with exactly 10 to go. Button blasted past D'Ambrosio and for three laps sat on the tail of Webber's Red Bull, gaining a DRS boost as he did so.
At the end of lap 64 Webber got it wrong at the last corner, and Button sliced past on the exit. Soon glued to Schumacher's tail, he used DRS to shoot past at the end of lap 65.
Despite having a pass at either end of it, on that lap he set an astonishing fastest lap of 1m18.866s – prior to that nobody in the race, even Jenson, had even got into 1m19s bracket!
"In those conditions a driver has to believe what he's doing, and has to be confident," said Whitmarsh. "He did a fantastic job. I think if you're in that zone you get the tyres at the right temperature. It's a virtuous circle. He was driving just fantastically, he was going to overtake anyone that was in his way."
With five laps to go, he was 3.1 seconds behind Vettel. And so the gap came down, to 1.6, 1.3, 1.1, despite the German improving his pace dramatically. At the start of the last lap, the margin was just 0.9.
"He popped through the field and we knew he had to put pressure on Sebastian," said Whitmarsh. "Sebastian's been driving great this year, he really hasn't made mistakes, but he hasn't been under so much pressure. You could see for three or four laps beforehand he was right on the ragged edge, and he was pushing very hard to try and keep the gap to Jenson."
We'll never know what Button could have done with DRS on the run to the final chicane on the last lap, but in the end, he didn't need it. Under the most extreme pressure, Vettel finally cracked – he slid wide at Turn Five, ceding the lead. Button charged past and took the flag 2.7s ahead after a performance for the ages.
"It felt like I spent more time in the pits than on the pit straight," he noted. "The guys did a great job of calling the strategy. At some points we definitely lucked out on the strategy, especially when the red flag came out, but we called it very well going to slicks.
"The car was working really well in these tricky conditions, so I enjoyed it very much coming through the field."
"I think the lesson is you don't give up until the last second of the race!," said a jubilant Whitmarsh. "You just keep pushing. Jenson with two incidents, two punctures, the drive through...
"It was a rollercoaster of a race, all in all. We just kept focus, and just finding a way through, trying to make the right calls for pit stops to get onto the right tyres at the right time. I think we got that just about right, and we made the best of it as a team. But ultimately Jenson was the guy who had to really drive decisively."