Roger Federer's dream of a potential US Open final clash with Novak Djokovic faces a stiff test on Saturday from Marin Cilic, the Croat who sees a first Grand Slam title as a perfect way to repair his reputation.
Federer, the 17-time major champion who is chasing a record sixth US Open title, has a 5-0 career edge over Cilic including a four-set win in New York in 2011 and at Toronto in three tough sets last month.
Cilic, the 25-year-old 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.
A six-month ban was eventually reduced to four by the Court of Arbitration for Sport, but Cilic still believes the entire process was unjust.
"It angered me how all the process went because it was not fair to me. It wouldn't be fair to any tennis player," Cilic said.
Cilic was a semi-finalist at Australia in 2010 and a two-time quarter-finalist in New York in 2009 and 2012.
But that final step has always proved impossible for Cilic, who now has 2001 Wimbledon champion and compatriot Goran Ivanisevic in his corner as coach.
Federer, the champion from 2004-2008, reached his ninth US Open semi-final but first since 2011 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.
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.
"I'm looking forward to playing Marin," said Federer. "He's a great guy. We had a tough, tough match in Toronto. I think I needed nine match points to close him out and beat him at midnight, 6-4 in the third, so we know what to expect."
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.
A win on Saturday would put him in a seventh final but first since 2009 when he was deposed as champion by Juan Martin del Potro.
World number one Djokovic, a seven-time Grand Slam title winner, faces Japan's Kei 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.
"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 old rival 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.
- Nishikori injury-free -
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.
The pair should have met in the semi-finals of the Miami Masters this year but Nishikori, having knocked out Federer, was forced to withdraw with a groin injury.
That was just one of four injury episodes in 2014 which also saw him quit the Madrid Masters final against Rafael Nadal. The back injury then contributed to a first round exit at the French Open.
"Kei is playing the best tennis of his life in the last 12 months. He started working with Michael Chang and he changed a few things in his game. 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 -- foot and hip surgeries in particular -- 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.
Nishikori, whose up and down season still saw him claim titles in Memphis and Barcelona, insists he has no physical problems, thanks to a tough cardio regime instigated by Chang, a Grand Slam title winner himself at the 1989 French Open.