The championship race remains wide open after Ryan Giggs headed United's equaliser barely a minute after Arsenal had grabbed a second-half lead.
The result leaves United three points clear of the champions, who have a game in hand.
But Arsenal will be hampered on the run-in by the loss of injured skipper Patrick Vieira - and suspended centre-back Sol Campbell, who was sent off for an 82nd minute elbow on Ole Gunnar Solskjaer.
Sir Alex Ferguson will be disappointed not to have left with three points after his side dominated most of the game. United, always prepared to scrap, took charge for all but a brief session after half time.
The difference between the sides was clear. Arsenal want to play beautiful football while United want to win.
Vieira, who limped off towards the end of the first half, is the only Gunners star who relishes a battle. United have repeatedly shown they can win while playing below their best.
Ruud van Nistelrooy's 23rd minute opener was typical of the chasm. He fought his way clear on the left, held off Martin Keown and dinked a shot over stand-in keeper Stuart Taylor. It was the sort of goal Arsenal, who specialise in cameos, rarely score.
Yet their 50th minute leveller was bizarre. Ashley Cole shot with his 'wrong' right foot. The ball hit Thierry Henry on the back of the legs and deceived Fabien Barthez.
Worse followed for United 12 minutes later. Henry looked a yard offside as he ran on to slot Gilberto Silva's throughball past Barthez, but the goal was allowed to stand.
Typically, Arsenal admired their lead instead of protecting it. How they miss the leadership and organisation that Tony Adams gave them for so long. Within 60 seconds, Giggs finished off Solskjaer's far post cross to set up a thrilling finale.
The game turned sour for Arsenal when referee Mark Halsey, alerted by an assistant, showed a red card to Campbell with seven minutes left. They may have gained a point on the night, but now they are playing catch-up in the title race.