Roger Federer has no doubt that his toughest test at the US Open will arrive when he takes on Stanislas Wawrinka in the semi-finals.

The second seed cruised to an emphatic 6-3 6-3 6-1 victory over Richard Gasquet to book his spot in the last four, and despite winning all five of his matches in New York without dropping a set, Federer is prepared for a battle against Swiss number two Wawrinka.

"I believe Stan can bring it, you know," the five-time winner told reporters. "That's my number one focus, that I make it as hard as possible for him to beat me.

"Personally I'm very happy with the where my game is at. It's just a matter of keeping it up and adjusting to Stan now."

Wawrinka progressed to the semi-finals with a comfortable win over Kevin Anderson on Wednesday night.