United boss Sir Alex Ferguson was left fuming at Williams after the Wales captain sent the ball crashing into Van Persie's head with the Dutchman on the ground after being fouled outside the box.
Ferguson launched a scathing verbal attack on Williams by insisting that he could have killed Van Persie and called for the Football Association to ban the defender.
Williams insisted it was not intentional and that he wanted to move on from the incident.
Williams and Van Persie were both booked after a melee involving the pair and Rooney takes a different view to Ferguson, feeling the referee Michael Oliver took the right decision only to book Williams.
"I think it's one of those things," he said. "The whistle's gone, the defender has gone to clear and it's hit him in the head. I think [it was] probably the right decision from the referee."