With scores locked at 0-0 and the Latics defending stoutly, the ageing midfielder fired home from close range after Ali Al-Habsi fumbled Nani's right wing cross.
The game went down hill from their for the Latics as the Premier League runners up managed to finish strongly and win the game 4-0.
Speaking about the afternoon's events, Manchester United manager Sir Alex Ferguson said: "Obviously as he has got older, he has not been able to do that. He doesn't need to do that now because we prefer him to play central midfield. But now he has scored on his 100th, 300th, 400th, 500th and 700th appearance. It is fantastic."
"Nick Powell is going to be a really good player. He has a great temperament. He has two feet and is quick. He is a great striker of the ball. For an 18-year-old boy it has been a terrific day.
"Alexander was a little bit rash at times but he has a great engine. He is raw and has a lot of rough edges. Hopefully we can develop that and he will be a really good addition for us."