Yet the score disguises a game where excitement was at a premium and good football came in only short sharp spurts. Forlan's goals were probably more memorable.
The Uruguayan did not enter the game until the 72 minute when he replaced van Nistelrooy.
He set up a golden opportunity for the disappointing Cristiano Ronaldo with his first touch, but saved the best for injury time.
With the game seconds over the 90 minutes Forlan hit a glorious left-foot shot from the right edge of the Villa box which screamed into the top left-hand corner of the net and put the Reds 3-0 up.
But Forlan was still not finished as, two minutes later, he collected a clever backheel from Kleberson just inside the Villa box before side-stepping Mark Delaney and placing his left-foot shot beyond keeper Thomas Sorensen and into the net.
Van Nistelrooy's brace came in the first half. In the 16th minute, he played a neat one-two with Ryan Giggs on the left.
Kleberson came into the action when his pass inside from the left edge of the Villa area set up van Nistelrooy to score with a well placed right-foot shot from 12 yards.
Van Nistelrooy's second goal stemmed from a 34th minute corner. Ronaldo crossed the ball from the left to find Giggs on the right side of the Villa box.
The Welshman knocked the ball into the centre and van Nistelrooy turned to score with a right-foot shot six yards out on the near post.
The goals apart, there was little to thrill the crowd, with Villa's only real chance coming from Lee Hendrie's 25-yard shot on the hour which was comfortably tipped over the bar United keeper Tim Howard.