Big-serving American John Isner has insisted that he has the credentials to overcome Roger Federer in the fourth round of the US Open on Monday.

Isner booked his spot in round four at Flushing Meadows after Jiri Vesely retired during their third-round match.

Federer, meanwhile, overcame Philipp Kohlschreiber in straight sets to advance into the next round.

Isner, 30, has said that the chance to take on Federer 'is why he plays the sport', but has insisted that being there is not enough as he prepares to overcome the Swiss.

"Yeah. It's going to be fun. It's what I work so hard for, to get an opportunity like this. On Monday I'm going to have fun with it. At the same time, I'm going to go out there and believe that I can win the match," Isner told reporters.

Isner's best showing at the US Open was in 2011, when he made the quarter-finals.