The world tennis number three Roger Federer saved two match points to defeat Frenchman Gael Monfils in a five set marathon to reach his ninth US Open semi-final, keeping alive his dream of a sixth title.
The 33-year-old Swiss is bidding to become the oldest winner of a Grand Slam title in more than 40 years.
Monfils, the 20th seed, had two match points in the 10th game of the fourth set but when Federer saved those Monfils lost his self-belief.
Federer will play the 16th seed, Croatian Marin Cilic in the semis.
Cilic toppled sixth-seeded Czech Tomas Berdych 6-2 6-4 7-6 to reach his first US Open semi-final.
Cilic, who missed last year's US Open as he sat out a doping ban, pounded 19 aces past Berdych, recovering an early break in the third to force the decider.
The other semi features top seed Novak Djokovic against Japan's Kei Nishikori.
The latest win means Federer is him just one win away from a career 600 victories on hard courts.
Federer's win was his ninth from two sets to love down and first at a major since he had to engineer a similar Houdini act against another Frenchman, Julien Benneteau, at Wimbledon in 2012 on his way to his 17th and most recent major title.
As Federer continued to struggle with the humid, windy conditions as well as his own shortcomings he uncharacteristically, lost his famed self-control in a testy exchange with umpire Carlos Ramos and even slammed his racket into the net at one stage.
If Federer wins the final it will be his 18th grand slam title.
Meanwhile Martina Hingis has turned back the clock to reach the US Open women's doubles final, 12 years after her last run to a title match at the majors.
The Swiss 33-year-old and her Italian partner Flavia Pennetta made the championship match with a 6-3 6-4 win over third seeds Sania Mirza and Cara Black, the India-Zimbabwe pairing.
Hingis last appeared in a doubles final at a Grand Slam in 2002 at the Australian Open, where she won the title with Anna Kournikova, one of nine doubles crowns she captured during her heyday
In the final Hingis and Pennetta, who are playing their first Grand Slam tournament together, will face Russian fourth seeds Elena Vesnina and Ekaterina Makarova for the title.