All things being equal, Roger Federer and Tomas Berdych will set up a semi-final at the US Open which both would relish and fear at the same time.

Yet their respective opponents in today's quarter-finals, Gael Monfils and Marin Cilic, are carrying momentum and have points to prove.

Some 10 months since he returned from a drugs ban, Cilic is enjoying a return to the kind of form that took him to his only previous semi-final, at the Australian Open in 2010. Initially banned for nine months for testing positive for a glucose supplement, he had his ban reduced to four months by the Court of Arbitration for Sport.

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The addition of Goran Ivanisevic, the former Wimbledon champion, as his new coach, at the end of 2013, seems to have done the trick as the Croat has stormed back up the rankings. His five-set win over Gilles Simon in the last 16 was his first over the Frenchman in five meetings and showed his new-found mental strength.

"I'm playing more consistently the last four, five months," he said, praising Ivanisevic for helping him with his serve. "That allows me to have more opportunities in the match on the return of serve, as I can be more aggressive and can play more risky."

Cilic beat Berdych in the third round at Wimbledon this year and said he was looking forward to the rematch. "For me he's not unbeatable but it's going to be a tough task. Quarter-finals in a major, I think for both of us, it's a good opportunity."

Ten years ago, Monfils won three of the junior grand slam titles and might have won all four but for a meltdown in New York, where Andy Murray emerged as champion. He made the top 10 in the senior game in 2011 and would surely have made more than his one grand slam semi-final at the French Open in 2008, had it not been for injuries and mental lapses.

Something seems different here, though, where he has reached the last eight without losing a set and keeping his energy levels intact. "I think I am hitting better the ball day after day," he said. "I am keeping simple things in my head, so obviously it is working.

"This is what I play tennis for: to play against a big legend, on a big court, in showtime," Monfils added.