Monfils seals quarter-final spot.

Gael Monfils will meet Roger Federer in the quarter-finals of the US Open after dismissing seventh seed Grigor Dimitrov.

Dimitrov, who ended Andy Murray's quest to defend his Wimbledon crown this summer, was considered the favourite to go through and meet five time champion Federer in the last eight but he suffered a 7-5 7-6 (8-6) 7-5 upset at the hands of the 20<sup>th seeded Frenchman.

Monfils is yet to drop a set in New York but appeared to let his frustration with his opponent and his own performance boil over. In their feisty encounter, the flamboyant Frenchman at one point stood directly on the service line and urged Dimitrov to serve before storming off court to his chair.

I just get a bit [angry]," Monfils said after his victory.

"Then I was sorry for Grigor, because I was in front and was like, 'Just serve because obviously I give you the game, so it's OK. Move it.'

"Sometimes when I get frustrated, when I don't like [something], I don't do it. It's nothing against anyone. I was upset."

Federer had no problems sealing his spot in the last eight as he eased past Roberto Bautista Agut of Spain in a 6-4 6-3 6-2 win at the Arthur Ashe Stadium. He and Monfils met just a month ago at the Cincinnati Open, where the Swiss had to dig deep to seal a tight 6-3 4-6 6-3 win.

In Tuesday's other quarter-final Marin Cilic defeated Gilles Simon in a five-set thriller to set up a clash with sixth seed Tomas Berdych, who strolled to a straight sets victory over Australian youngster Dominic Thiem.

In the women's singles, Caroline Wozniacki eased into the semi-finals, barely breaking a sweat as she crushed Italy's Sara Errani 6-0 6-1 in just over an hour. The Dane will meet Peng Shuai of China in her final four clash.

Serena Williams meets Flavia Pennetta while Victoria Azarenka takes on Ekaterina Makarova in the other quarter final clashes on Wednesday.