Tyler Blackett's 82nd-minute own goal denied Manchester United a win against Arsenal which would have taken them above the Gunners in the table this afternoon.
The two sides will both be in the Champions League next season, but Arsenal have the upper hand in the battle for a top-three spot which would secure automatic qualification for the group stage.
Both sides started today's game cautiously, with the first shots at goal arriving just after the 10-minute mark as Radamel Falcao and stand-in skipper Chris Smalling both had their efforts deflected off target.
Not long after, United playmaker Juan Mata had the first shot on target, but his free kick from 20 yards was tame and straight at David Ospina.
Arsenal didn't manage a shot of any kind in the first half - the first time in over 10 years that they've failed to do so - but striker Olivier Giroud was almost gifted two chances by Phil Jones.
First, the England defender lost his footing but was lucky to see the Frenchman take a bad touch before he was close to passing the ball past onrushing goalkeeper David de Gea to put Giroud through on goal.
United broke the deadlock just before the half-hour mark through Ander Herrera. The Spaniard was left all alone at the back post as Marouane Fellaini commanded the attention of two defenders, allowing Herrera plenty of time to fire home Ashley Young's deep cross for his sixth goal of the season.
It was the first time since New Year's Day that Arsenal had conceded a first-half goal in the Premier League.
Daley Blind was close to doubling the hosts' lead just before half time, but his low shot was inadvertently blocked by teammate Smalling.
Arsenal's first shot arrived five minutes into the second half, but it didn't test De Gea as Alexis Sanchez wildly blazed high and wide with a volley.
Falcao was chosen ahead of Robin van Persie to start in Wayne Rooney's absence, but he lasted just an hour as Van Persie replaced him. It was probably the Colombian's last appearance as a United player at Old Trafford and he waved goodbye to the supporters as he left the field.
Arsenal finally carved out a good chance moments later. Giroud did well to take Ramsey's pass in his stride, but he couldn't beat the sprawling frame of De Gea from close range.
That gave the Gunners a lift and they had their best spell of the match as Ramsey was twice denied a shooting opportunity by Marcos Rojo, while Santi Cazorla lost his footing just as he was about to fire at goal.
United suffered a blow with 15 minutes to go when De Gea trudged off injured. His departure meant a debut for former Barcelona goalkeeper Victor Valdes and he was soon picking the ball out of the back of the net.
Arsene Wenger had thrown on Theo Walcott just before Valdes's introduction and the England winger played a key part in the visitors' equaliser. He collected a long-range pass and fired over a cross that Blackett, another substitute, diverted over Valdes and into the far corner.
United have never lost a home Premier League game after leading at half time, but Arsenal almost completed the turnaround in the final 10 minutes when Giroud stroked into the side-netting from close range.
Van Persie had United's best chance in the closing stages, but he couldn't extend his streak of scoring against Arsenal at Old Trafford to three games as he fired over.
Arsenal haven't beaten United in eight attempts in the Premier League, but stay two points clear of the Red Devils in the table and will all but seal a top-three finish by avoiding defeat against Sunderland in midweek.
