Ole Gunnar Solskjaer suffered his first premier league defeat since being appointed Manchester United’s interim manager as Arsenal leapfrogged their opponents to move into the top four.
Switzerland midfielder Granit Xhaka beat David De Gea with a swerving shot from outside the penalty area, which the United keeper was expected to stop.
Romelu Lukaku hit the bar while the game was goalless when it appeared easier to score and soon after arsenal took the lead.
Brazilian midfielder Fred also struck the post for United.
With the win Arsenal moved to the 4th position on the log with 60 points while United dropped to 5th.