Djokovic sets up a potential quarter-final against Federer
Novak Djokovic has sweated his way to a 6-3, 6-4, 6-3 fourth round win over Joao Sousa as the heat returned to the US Open, potentially setting up a mouth-watering quarter-final meeting with Roger Federer.
Djokovic did his part, improving his perfect record in US Open fourth-round contests to 11-0, leaving it to Federer — who will take on Australian John Millman in the late contest on Arthur Ashe Stadium court — to give the fans what would be a hotly anticipated matchup.
A Federer-Djokovic clash would provide the perfect contest to herald the business end of the tournament, with the two champions having claimed seven titles at Flushing Meadows between them.
The first Portuguese player to reach the fourth round of any grand slam, the 68th ranked Sousa never looked a threat to progress any further as his magical US Open run came to an end.
The biggest concern for Djokovic might well have been the conditions as the heat returned to New York after a few days of relief.
Through his opening-round matches, Djokovic and his play both suffered under a blazing sun and with temperatures nudging 32 degrees Celsius, the extreme conditions took a toll on 31-year-old Serb.
The sixth seed went off court two sets and 2-1 up for a medical evaluation.
The 13-times grand slam winner had made easy work of the opening set, breaking Sousa twice, the second time to close out the set.
Things grew tougher in the second as a sluggish Djokovic laboured before again clinching the set with a break.
As the temperatures rose so did the tempers, with both players engaging in animated arguments with chair umpire James Keothavong.
Djokovic, however, was able to keep his cool just long enough to finish off Sousa with another late break.
Kei Nishikori will be hoping to make another deep run at his most successful Grand Slam event after he easily outclassed Philipp Kohlschreiber 6-3, 6-2, 7-5 to reach the quarter-finals.
Nishikori will come up against Alex de Minaur's conqueror Marin Cilic, after the seventh-seed powered past David Goffin, 7-6 (8-6), 6-2, 6-4.
Last year's finalist marches on
In the women's draw, Madison Keys eased into the quarter-finals with a 6-1, 6-3 victory over Slovakia's Dominika Cibulkova.
The 14th-seeded American, looking to go one better than her runner-up finish at Flushing Meadows last year, relied on both her dangerous serve and powerful groundstrokes to deny Cibulkova any chance of an upset win.
Cibulkova, who arrived on the Arthur Ashe Stadium court brimming with confidence after toppling Wimbledon champion Angelique Kerber in the previous round, countered with a similarly aggressive game to little avail.
With the US Open's heat advisory put back into effect, the pair traded punishing groundstrokes under the blazing sun and it was Cibulkova who was often pinned well behind the baseline and at the mercy of her opponent.
Keys has been solid in New York, having dropped a single set through four matches, and turned it up a notch against her 29th-seeded opponent as she lost only 10 points on serve during a 76-minute match in which she was broken once.
Cibulkova, who had not reached this stage of the year's final grand slam since reaching the last eight in 2010, pulled ahead 3-2 in the second set but Keys stormed home from there and clinched the win on her second match point when the Slovak sent a forehand wide.
With the win, Keys improved to 5-0 lifetime against Cibulkova and becomes only the second woman, after Kerber, to reach the quarter-finals or better at three of the four grand slams this year.
Next up for Keys, who was routed by Sloane Stephens in last year's final, is the winner of the evening clash between five-times grand slam champion Maria Sharapova and Spanish 30th seed Carla Suarez Navarro.
Elsewhere, Japan's Naomi Osaka reached her first grand slam quarter-final by beating Aryna Sabalenka 6-3, 2-6, 6-4 in a pressure-packed clash of two hard-serving 20-year-old prospects.
An emotional Osaka wiped tears from her eyes in an on-court interview, thanking the crowd and saying she would not have forgiven herself had she lost.
"I was just thinking I have to fight for every point; even if I break a leg I should try to get to every ball," she said.