كتب : Sherif Tarek
The South Korean winger connected with a Nani cross, lifting the ball over the head of Gunners' polish goalkeeper Wojciech Szczesny and into the net in the 41st minute.
Wayne Rooney squandered a penalty kick 18 minutes from time, after Nani was felled in the area by Gael Clichy.
United are now on top of the league table with 34 points, two ahead of second-placed Arsenal.
The Red Devils have one more game in hand against Blackpool.