Manchester United endured a disappointing day in North London as the Reds suffered a first Premier League defeat since October with a 2-0 loss to Arsenal.
Two second-half goals in quick succession proved decisive for the Gunners as Granit Xhaka and former United striker Danny Welbeck got on the scoresheet.
Jose Mourinho made eight changes to his United line-up that beat Celta Vigo on Thursday with Juan Mata making his first start since returning from groin surgery and young defender Axel Tuanzebe given his full Premier League debut.
With the unbeaten league run standing at 25 games ahead of kick-off, the Reds were looking to close the gap on the top four to just one point with Liverpool dropping two points at home to Southampton earlier in the day.
It was a bright start from both sides and United had a first sight of goal inside two minutes when Mata’s cross from the right found Wayne Rooney, only for the United captain to head over.
With both sides needing a win to keep pace in the race for the top four, it soon became an end-to-end encounter with Aaron Ramsey first going close for the hosts after a clever through ball from Alexis Sanchez allowed the Welshman to force De Gea into an outstanding low save to his right.
Welbeck led the line for the Gunners and just before the half-hour mark he controlled the ball with his back to goal inside the six-yard box, turned to shoot but it was smartly blocked by a lunging Phil Jones.
That chance ignited Arsenal and they went close again moments later when Alex Oxlade-Chamberlain picked up the ball 25 yards out and rifled an effort, which took a deflection, straight at De Gea who palmed it to safety.
