Roger Federer
Federer moved into a record 36th grand slam semi-final at Flushing Meadows. Getty Images/Chris Trotman

Roger Federer staged a dramatic comeback after saving two match points to reach the US Open semi-final after defeating Gael Monfils in five sets at Flushing Meadows.

The Swiss recovered from two sets down for the ninth time in his illustrious career to prevail 4-6 3-6 6-4 7-5 6-2 and deny Monfils just his second appearance in the last four of a grand slam.

The 28-year-old Monfils had dominated the opening exchanges and was presented with two opportunities to complete a straight sets victory but was eventually blown away by a virtuoso Federer performance.

The 17-time major champion will continue his pursuit of a record-equalling fifth US Open title in his 36th grand slam semi-final against Marin Cilic after he defeated Tomas Berdych in three sets.

"I still thought the finish line was far for Gael," said Federer.

"I knew I could play better tennis. When I was down two match points, that's when I wasn't feeling too good any more.

"I thought 'this is it, don't let him have an easy shot, and go down fighting.' But I served well and managed to turn it around.

"It's just unbelievable to win matches like this at Slams," the former world No.1 added.

"I have won other big ones in other places but over best-of-five, saving match points against Gael in an atmosphere that it was out here tonight, it's definitely very special.

"I'm not sure I have ever saved match point before in a Slam. If that hasn't happened, I'm unbelievably happy that it was today."