Vince Vaughn -- Buys Lane Kiffin's Beach Mansion

Lane Kiffin's loss is Vince Vaughn's gain ... because the "Wedding Crashers" star has been ID'd as the mystery buyer who paid $6.5 million for the Manhattan Beach pad Lane Kiffin sold when after he was fired from his gig at USC.

Don't feel bad for Lane ... he pocketed a cool $1 MILLION from the sale.

And don't feel bad for Vince either ... he gets to move in to one of the coolest mansions on the beach -- a 7,308-square foot palace with state-of-the-art everything and a kick ass backyard.

Everyone wins ... which wasn't happening when Lane was living IN the house.