Roger Federer and Novak Djokovic can set up a dream US Open final on Saturday but standing in their way are the unlikely figures of Marin Cilic and Kei Nishikori.
Federer, the 17-time major champion who is chasing a record sixth US Open title, is back in the semi-finals for the first time since 2011 and looking for a return to the final which he last graced in 2009 when his five-year winning streak was snapped by Juan Martin del Potro.
He takes a 5-0 career edge over Cilic into their showdown, a record which includes a four-set win in New York in 2011 and at Toronto in three tough sets last month.
"He's done well in the past. It's not like he's come from the top 50 to all of a sudden be knocking on the top 10 door," said Federer of his 25-year-old opponent who was a semi-finalist at Australia in 2010 and a two-time quarter-finalist in New York in 2009 and 2012.
"I think he's doing all the right things, Marin. I played him in Toronto. Funny match. I didn't play great in the first set but somehow got it done, and then I think I wasted like eight match points in the second set; had to go three."
Cilic, the 14th seed, missed last year's US Open sitting out a controversial doping ban handed out after he tested positive for a banned stimulant contained in a supplement bought over-the-counter by one of his staff.
Federer, the champion from 2004-2008, reached his ninth US Open semi-final with a dramatic 4-6, 3-6, 6-4, 7-5, 6-2 win over France's Gael Monfils, saving two match points in the process.
In a career of firsts, it was the first time he had saved match points at a major and gone on to win.
The 33-year-old Swiss lost the Wimbledon final in five sets to Djokovic in July and is playing in a 60th consecutive Grand Slam tournament.
Federer has already improved on his last two visits to New York -- a quarter-final exit to Tomas Berdych in 2012 and a dispiriting fourth-round loss to Tommy Robredo 12 months ago.
World number one Djokovic, a seven-time Grand Slam title winner, faces Japan's Nishikori in Saturday's first semi-final.
It's the Serb's eighth consecutive US Open semi-final having shrugged off his early losses in the Masters events at Toronto and Cincinnati, understandable hangovers from his second Wimbledon win.
- History for Japan -
"I was aiming to play my best tennis in the US Open, and I knew that's going to happen," said Djokovic whose post-Wimbledon slump was hardly surprising with so much energy invested in his wedding and impending fatherhood.
Djokovic, who has made the last four finals at the US Open, won an intense physical battle against Andy Murray in the quarter-finals in a four-set triumph which showcased his rock-solid defensive skills -- he saved eight of 12 break points he faced -- as well as his stamina.
Djokovic and Nishikori have only met twice with the Serb winning in straight sets at the 2010 French Open before the Japanese star gained revenge with a semi-final triumph on the Basel hard courts one year later.
"Kei is playing the best tennis of his life in the last 12 months. He serves very efficiently. Obviously he's very, very fast, maybe one of the fastest on the tour," said Djokovic.
Nishikori, whose career has endured a number of medical stop-starts has been pain-free in New York, his impressive stamina taking him past Milos Raonic and Australian Open champion Stan Wawrinka in successive five-set duels.
They were his first back-to-back wins over top 10 players at a major and both were achieved in matches lasting more than four hours.
The 24-year-old Nishikori is the first Japanese man to make the semi-finals since Ichiya Kumagae in 1918 when the US Championships were played at nearby Forest Hills.
Saturday's semi-finals also see four former Grand Slam champions in the coaching corners -- Boris Becker with Djokovic, Stefan Edberg in Federer's team, Goran Ivanisevic is coaching Cilic while Nishikori is being coached by Michael Chang.