Robin van Persie has scored 25 league goals for Manchester United, or 29 in all competitions, but the latest threatens to have considerably more impact for his old club than his current one. If Arsenal are to miss out on the Champions League next season – something that has not happened in the past 15 years – they will look back with some anguish on that moment when their former player had the ball in his hands and a crowd that once revered him probably knew what was coming next.
There was considerable pressure on Van Persie for that penalty, back in a stadium where he is now largely reviled, acutely aware of the schadenfreude that would follow if he lost his nerve.
The volume had gone up several notches as Arsenal's supporters did their best to put him off. Yet they should probably have known he is not a man to be put off easily. Van Persie's shot was struck with power and precision, beating Wojciech Szczesny to his left. There was a strategic lack of celebration but the walk back to the centre circle was bristling with defiance.
A draw was probably a fair result but neither side could be satisfied. Arsenal have fallen behind Chelsea into the fourth Champions League qualifying place, two points ahead of Tottenham Hotspur but having played a game more. Arsène Wenger's team were considerably the better side in the opening stages. Yet their inability to build on Theo Walcott's goal should gall them when United were there for the taking in the first half. Add in the Van Persie factor and the Emirates was full of exasperation at the final whistle.
For United, the opportunity to set a record and overtake Chelsea's 95 points, from José Mourinho's first title-winning side in 2005, is gone. The game could have gone either way in the second half but it was an erratic performance from the champions and rare to see them look as dishevelled as they had in the opening 40 minutes.
Martin Keown, Arsenal's guest of honour, summed it up when he was invited on the pitch at half-time to offer his thoughts. United, he said, looked like they had been doing a lot of celebrating.
Ferguson denied that, as you would expect, and his main criticisms were with the referee, Phil Dowd, for the frequency with which he kept brandishing his yellow card. Five of United's players were booked, including four in a grumpy 13-minute spell, and three from Arsenal.
Bacary Sagna was extremely fortunate not to be sent off just before the hour. The full-back had already been shown a yellow, having given away the penalty, and his sliding challenge on Patrice Evra should have brought a red. Instead, Dowd waved play on and did not return to the incident at the next break in play.
United also had legitimate arguments about Walcott being offside for his goal even if they should not probably linger on it too much given they have benefited from some generous decisions themselves lately. In fairness to Dowd, his judgment was impeccable for the penalty because, at the speed it was, it was anything but a straightforward decision. Van Persie had run through the left-hand channel, latching on to Sagna's mistake, and the defender's attempt to make amends, sliding in, was asking for trouble. He missed the ball, but only very marginally, before taking Van Persie's ankles.
For Van Persie, that goal might have had therapeutic qualities. It had been his loose pass that gave Arsenal the ball to go ahead, playing it straight to Kieran Gibbs and then watching as a quick exchange of forward passes via Mikel Arteta and Tomas Rosicky left Walcott running into the penalty area. Rosicky's through ball was perfectly weighted inside Evra and Walcott took advantage of the lack of a flag to drive an angled shot past David de Gea.
Arsenal were well on top for the next half an hour, quicker to the ball, playing with width and fluidity and pinning back their opponents for long enough to feel they really ought to have made more of their superiority.
They lacked a bit of presence in attack, with Olivier Giroud suspended and Lukas Podolski not greatly effective, but their desire to press forward in numbers, from all different angles, made them a constant threat.
United took a long time to get going and, at times, were shabby in the extreme. Rafael da Silva and Phil Jones, in quick succession, passed the ball out of touch under no pressure. De Gea dropped a corner and made a hash of a clearance. Wayne Rooney improved after the break but was barely involved before then. Nani was on the edges, Antonio Valencia even more so. Ferguson erupted at one stage after Dowd waved play on despite Arteta and Aaron Ramsey both checking Nani's run. It was a bad decision but it was tempting to wonder whether Ferguson's real ire stemmed from the way his team were playing.
The paradox, and perhaps a measure of the way this Arsenal side defend sometimes, is that United could still reflect on some decent opportunities of their own before Van Persie's equaliser. Jones, driving through midfield in a manner reminiscent of a young Bryan Robson, headed two good chances wide with considerably less distinction.
Then a moment when the Emirates held its breath, as Nani clipped a wonderful cross into the penalty area and Van Persie was alone inside the six-yard box. Szczesny's sprawling save to keep out the header, from point-blank range, was exceptional. Van Persie, however, was not finished.
Man of the match Rio Ferdinand (Manchester United)