NEW YORK -- Roger Federer saved two match points while coming all the way back from a two-set deficit to beat Gael Monfils 4-6, 3-6, 6-4, 7-5, 6-2 Thursday night and reach the U.S. Open semifinals for the first time since 2011.
Frustrated by Monfils' unpredictable style, flummoxed by the swirling wind, and missing shots he normally makes, Federer twice was a single point from losing while down 5-4 in the fourth set.
But he got out of that hole, starting a five-game run that put the match in his control for the first time all evening. It helped that Monfils' quality of play dipped, including what wound up being a total of 10 double-faults.
This was the ninth time Federer has won a match after dropping the opening two sets.
The 20th-seeded Monfils was trying to reach his second career Grand Slam semifinal. Instead, Federer advanced to his 36th, ninth at Flushing Meadows. Five of Federer's record 17 major singles titles have come at the U.S. Open, but he exited in the quarterfinals in 2012, and the fourth round in 2013.
On Saturday, the second-seeded Federer will play 14th-seeded Marin Cilic of Croatia. The other semifinal will be No. 1 Novak Djokovic against No. 10 Kei Nishikori; their quarterfinal victories came Wednesday.
Cilic wasn't allowed to play in last year's U.S. Open, forced to the sideline by a four-month doping suspension that he says he didn't deserve. But Cilic reached the second Grand Slam semifinal of his career, and first since 2010, by beating sixth-seeded Tomas Berdych of the Czech Republic 6-2, 6-4, 7-6 (4) Thursday.
"I mean, it was a difficult period. I didn't know when I'm going to start back. But (it) was also (a) good period for me," Cilic said. "I matured a bit more and I was working, day after day."
His quarterfinal ended hours before the other began, and Cilic probably assumed he would wind up facing Federer next.
But that did not seem a certainty through the first 78 minutes of Federer-Monfils. That's how long it took Monfils to shake off a twisted ankle and build a two-set lead, assisted by Federer's 26 unforced errors in that span.
At 33, Federer was participating in his 43rd Grand Slam quarterfinal, while Monfils - who turned 28 on Monday - was in only his sixth. And Monfils had only won one of those, at the 2008 French Open, where he then lost to Federer in the semifinals, part of the Frenchman's 2-7 head-to-head record coming into Thursday.
The air was swirling in the cavernous arena, rippling the players' shirts and the giant American flag atop the stadium. In the early going, Monfils' whiplike forehand was able to cut through the wind.
As the clock was about to strike 11 p.m., Monfils held two match points at 5-4 in the fourth set, with Federer serving. On the first, Monfils had an opening for a backhand passing shot, but it flew long. On the second, Federer produced a forehand winner, and the crowd roared.
After Federer held there for 5-all, Monfils had a letdown, double-faulting twice in a row to get broken. Soon enough they were in the fifth set - which began with another break by Federer.
By then, he was on his way.
Make no mistake, though. This was not easy. The turnaround might not have been possible for Federer a year ago, when he was dealing with a bad back and trying to figure out whether he should switch to a larger racket head.
But now Federer, however old, is approaching his skills of old. He has made the finals at his previous four tournaments, the first such run by a 30-something since Ivan Lendl in 1990.