After a scoreless first half, Paul Scholes broke the deadlock by tapping home after Al Habsi had only been able to parry Nani's low cross into his path.
On his 700th United appearance, it extended a remarkable record.
"That is what we always remember about Paul, the way he ghosts into the penalty box," said Sir Alex Ferguson.
"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."