By Sky Sports
Arsenal seized the initiative in the race for the top four with a 2-0 victory over Manchester United that inflicted the first league defeat of Ole Gunnar Solskjaer's tenure.
Granit Xhaka forced an uncharacteristic goalkeeping error from David de Gea as his swerving shot fired the Gunners in ahead inside 12 minutes before Pierre-Emerick Aubameyang's penalty made sure of the victory midway through the second half.
United hit the woodwork twice in the first half but there was a clear hangover from Wednesday's Champions League heroics in Paris as they suffered their first Premier League defeat December 16.
Arsenal leapfrog United into fourth as a result of their ninth-successive home victory and move to within a point of third-place Tottenham as the top-four race intensifies with eight games to play.
Arsenal had United under the cosh early on, registering three attempts, all of which were off target, inside the opening nine minutes, but United's first effort nearly yielded the opener.
Luke Shaw strode down the left flank and picked out Romelu Lukaku in the Arsenal area, but the Belgian could only divert the ball onto the crossbar before Paul Pogba's attempted rebound was blocked.
Arsenal then took a deserved lead, albeit in bizarre circumstances, as Xhaka swerving shot from 25 yards wrong-footed De Gea on its way into the middle of the United goal.
United almost drew level on the stroke of half-time as Pogba, Shaw, Lukaku and Dalot combined at pace on the counter and rolled the ball into the path of Rashford in the Arsenal area, but Xhaka intervened with a crucial block to preserve the Gunners' lead.
Leno then came to Arsenal's rescue six minutes after the interval, racing off his line to confront Lukaku after Rashford's superb side-rule pass presented the Belgian with the chance to equalise, but the German diverted it onto the roof of the net.
It looked as though United had settled into a rhythm that would cause Arsenal problems but, instead, the Gunners doubled their lead as Aubameyang - eight days on from his missed north London derby penalty - converted from 12 yards after Fred had bundled Alexandre Lacazette to ground.
On a day where Aston Villa's Jack Grealish was attacked by a Birmingham fan running onto the field of play, an Arsenal supporter appeared to run into Chris Smalling as he invaded the pitch after Aubameyang's goal.
Lacazette should have put the game out of sight on 71 minutes with Arsenal's third but he fired wide after Victor Lindelof's misreading of the ball presented him with a clear route to goal, though it did not cost the Gunners as they saw out a comfortable victory.
Unai Emery: "I'm very proud of our supporters, they pushed us a lot and this is a big result and they created a big atmosphere for our players. United were in a good moment after one result against PSG but we had a big performance and we are in a good moment in the Premier League. To take three points and get a good position for our target is very good and I'm happy for the players."
Ole Gunnar Solskjaer: "We started slowly, maybe a backlash from Wednesday night, but we created chances and when they get the first goal it becomes a different game. We created so many more chances than when we beat them in the FA Cup. Sometimes it happens, we hit the woodwork twice and had five very big chances ourselves. We just had to go for it towards the end, but we were not really at it and it is one of those days where you have to dust yourselves down from."