Eddie Nketiah struck in the closing moments against United to claim a dramatic victory for Premier League leaders Arsenal.
Eddie Nketiah struck in the closing moments against United to claim a dramatic victory for Premier League leaders Arsenal, who retained a five-point advantage over Manchester City as a result of their late winner.
City had earlier seen off Wolves 3-0, with the prolific Erling Haaland netting a fourth hat-trick of the season.
That put the ball in the Gunners’ court and they were tied 2-2 against United in an entertaining encounter that looked like costing them some of their advantage at the summit.
Nketiah had earlier equalised after Marcus Rashford’s fine drive took his post-World Cup tally to nine goals in as many games. Bukayo Saka put the hosts ahead in the second half, before Lisandro Martinez opened his Red Devils account with a looping header.
That looked to be enough to secure a point but, with time ticking, Nketiah’s improvised finish – flicking out his right boot and turning home Martin Odegaard’s deflected shot from close range – sparked joyous celebrations.
While Keane acknowledged the strides United have made under manager Erik ten Hag this season, he didn’t hold back as he named Luke Shaw, Aaron Wan Bisakka, Fred and Scott McTominay as their weak links against the Gunners.
"United have made progress but at the end of the game, I'm looking at Shaw still at left-back - there are questions over him,” he told Sky Sports.
"Wan-Bissaka, Fred, McTominay - it's like Manchester United haven't moved on from the problems in the past.
“I'm not blaming them as it was a tough game, give credit to Arsenal. It was a reality check.
"I still think United are well short. They were missing players today but a squad like United should be able to deal with it.
"Then when the going got tough you are looking at the bench and it wasn't great.
"For all the money United have spent they are still well short. I think they are certs for top four, maybe win a cup, but in terms of competing for league titles there is a way to go."
Keane’s belief that United contributed to their own downfall at Arsenal was backed up by the forceful words of United manager Erik ten Hag.
"We have to face that and learn the lessons. We've made mistakes. All the three goals, we could avoid them. Normally we are better in such situations,” said the Dutch coach.
"It's tough, that's quite clear. You could smell it. There were moments on the break, but we have to defend much better.
"We are making the wrong decisions - not one player but many players. You concede the third goal same as the first two goals.
"We started the game very well, we score the goal, we're leading and then we make mistakes that are unacceptable. Today we have to accept, learn the lessons and move on.
"The two first goals we're making so many mistakes. It can't happen. That is a lesson we have to take.
"We will face the players with this because it can't happen. Good teams don't make such mistakes. Again, not one player. We make many mistakes.
"This can be a reality check.We are unsatisfied on this defending performance. We can do better.
"Last week we kept the opponent more away from our box, but if they were in the box we defend much better. Normally we don't concede goals from corners - today, two.
"The last goal so short before the end of the game. That is not acceptable.
"I've said the same words in the dressing room - if you want to win you can't make the mistakes I've just mentioned."