Arsenal inflicted Ole Gunnar Solskjaer's first domestic defeat as Manchester United caretaker manager to leapfrog their opponents into the Premier League's top four with a vital 2-0 victory at the Emirates on Sunday.
Granit Xhaka's early strike and Pierre Emerick-Aubameyang's penalty 21 minutes from time moved the Gunners into fourth, two points above United in fifth.
Unai Emery's men also close to within just a point of third-placed Tottenham and now hold the upper hand in the race for Champions League qualification.
Arsenal do not face any of the top six in their remaining eight league games, whilst United host title-chasing Manchester City and Chelsea in the coming weeks on top of their Champions League and FA Cup commitments.
European trips to France for both sides in midweek produced vastly contrasting results as United shocked free-spending Paris Saint-Germain 3-1 to progress to the quarter-finals of the Champions League.
The Gunners on the other hand went down 3-1 to Rennes to give themselves a mountain to climb in Thursday's second leg to reach the last eight of the Europa League.
Emery made five changes from that side and was rewarded with a fast start that could have been rewarded inside two minutes had Alexandre Lacazette connected with Sead Kolasinac's wicked cross.
However, Arsenal were nearly hit with a sucker punch when with United's first attack, Romelu Lukaku turned Luke Shaw's cross onto the crossbar for the first of a series of wasted chances for the Belgian striker.
David de Gea made 14 saves as the Red Devils won 3-1 at the Emirates last season in one of the Spaniard's best ever United performances.
But for once De Gea was found wanting for the opening goal as he failed to read the swerve on Xhaka's long-range strike.
United seemed to feel the after-effects of their heroics in Paris early on, but soon clicked into gear to look more like the side that had suffered just one defeat in Solskjaer's first 17 games in charge.
Fred's curling effort from outside the box clipped the post before Lukaku's dangerous cross just evaded Marcus Rashford at the back post.
Solskjaer spoke on Friday of his excitement that Lukaku and Rashford could form a potent partnership and there was more evidence of their understanding when the England international played in his strike partner moments later.
Lukaku tried to round Bernd Leno, but the Arsenal goalkeeper stood up well to block.
The German stopper had an unconvincing start to life as Arsenal number one, but has looked ever more assured in recent weeks and made another huge save to deny Lukaku once more from close range six minutes into the second-half.
United were utterly dominant for the first 20 minutes of the second period as Rashford also sent a dipping free-kick inches wide, but Arsenal hung on and then got a break 22 minutes from time.
Lacazette charged into the area and hit the floor under minimal contact from Fred, but enough for referee Jon Moss to point to the spot.
Aubameyang missed a last-minute penalty to win the north London derby against Tottenham last weekend, but made no mistake to leave the visitors a mountain to climb.
Solskjaer's time at United as a player and over the past three months has been littered with late drama.
However, there was no turnaround this time to leave the Norwegian with plenty of work to do just to qualify for next season's Champions League.
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