Jlloyd Samuel set the visitors on their way with an own goal seven minutes before the break and a Dimitar Berbatov brace and further strike from substitute Darron Gibson sealed the rout.
But it was Van der Sar who was singled out by Ferguson as the match-winner for his crucial first-half saves from Johan Elmander and then Fabrice Muamba.
He told ESPN: "They were absolutely magnificent saves. The second one in particular I think was a match-winning save."
Portugal winger Nani set up two of the United goals and he too impressed his boss.
"Nani's been playing like that for weeks now," he said. "He has hit form at a terrific time for us. He's made two goals.
"We're very pleased he's signed a new contract for another four years. He's young. He's maturing."
Ferguson claimed it had been a hard day's work for his team despite the comfortable-looking scoreline.
"The times we did get the ball down we did play some good football," he said. "I'd like to have seen more of it but it was a very difficult game."
The result saw United finish the day a point clear of Chelsea, who were 7-1 winners against Aston Villa this afternoon, and four ahead of Arsenal, who drew 1-1 at Birmingham.
"It was a bad one for Arsenal to drop points so late in the game," said Ferguson. "They're now four points behind us.
"I said yesterday we'll all drop points but the name of the game is to make sure you don't drop as many as the rest."
Bolton boss Owen Coyle claimed the scoreline flattered the visitors but admitted his side had switched off and lost concentration.
"I'm disappointed with the defeat and the manner of the defeat late on," he told ESPN. "That's what happens when you play against the best teams. If you switch off and gift them goals as we did you're going to be punished.
"But for 70 minutes of the game I thought we were terrific.
"There was a lot of things we could have done better. The scoreline flatters Manchester United - no doubt about it.
"We were the architects of our own downfall."