Arsenal took the lead in bizarre fashion in the 13th minute when from a corner United keeper David de Gea went down clutching his foot after he was stood on by team mate Fred and Emile Smith Rowe drilled a shot into the unguarded goal from the edge of the box.
As referee Martin Atkinson had not blown his whistle before the ball went into the net and no foul had taken place, the goal stood.
The Gunners struck back quickly through Martin Odegaard but Ronaldo got the winner from the penalty spot after Atkinson went to the pitchside monitor and ruled that Fred had been brought down by Odegaard.
The match began with United fans displaying a tribute banner to former manager Ole Gunnar Solskjaer who was sacked last month. The club’s new interim manager Ralf Rangnick watched the game from the stands. Michael Carrick, who announced that he will be leaving the club after the match, finishes his interim spell as manager undefeated after two wins and a draw.