Roger Federer rallied three straight sets after he lost the first two sets to win against Gael Monfils at the quarterfinals of the U.S. Open in Flushing Meadows on Thursday night.

The Cincinnati Masters titlist had his back against the wall as Frenchman Monfils took over the first two sets but the 17-time Grand Slam champion stormed back, thanks to 10 the double faults from Monfils and the added factor of fatigue, to win the match, 4-6, 3-6, 6-4, 7-5, 6-2.

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This is the ninth time that the 33-year-old Federer have been in this situation wherein he is down by two sets and emerge victorious.

The match lasted three hours and 20 minutes, and has taken a toll on Monfils who was obviously committing more unforced errors as the match progressed to the fifth and deciding set.

Federer was serving in the fourth set and was down 4-5 when Monfils had the opportunity to win the match but the Swiss saved two match points and completely turned it around.

"When I was down two match points, that's when I wasn't feeling so great anymore," Federer said. "But I stayed in the match and somehow turned it around."

The second seeded Federer reached the tournament's semi-finals again since 2011 and will face Marin Cilic who defeated Tomas Berdych earlier and reached his first semis of the tournament in straight sets, 6-2, 6-4, 7(7)-6(4).

The powerful 14th-seeded Croatian converted 19 service aces and 46 winners to dispatch the sixth-seeded Czech in two hours and 12 minutes.

"I feel I'm playing probably the best tennis of my career," said Cilic.

Federer is heavily favored to win against Cilic whom he lost to in the third round of the tournament in 2011.

Federer hopes to achieve his 18th Grand Slam title and is on track to face World No. 1 Novak Djokovic to setup a Wimbledon finals rematch.

TagsRoger Federer, Gael Monfils, Marin Cilic, Novak Djokovic