US Open PIX: Djokovic, Cilic Keys march into quarters

IMAGES from Day 8 of the US Open on Monday

Novak Djokovic sweated his way to a 6-3, 6-4, 6-3 fourth round win over Portugal's Joao Sousa as the heat returned to the US Open on Monday, setting up a potential quarter-final with second seed Roger Federer.

Djokovic improved his perfect record in US Open fourth round contests to 11-0, leaving it to Federer, who plays Australian John Millman in the late contest on the Arthur Ashe Stadium court, to give the fans a mouth-watering match-up.

A Federer versus Djokovic clash would provide the perfect contest to propel the US Open into the second week, with the two champions having claimed seven titles at Flushing Meadows between them.

"The matches I've played against him (Federer) have shaped me into the player that I am today," said Djokovic, who beat the Swiss at the Cincinnati final in the lead up to the US Open.

Sousa arrived at the season's final Grand Slam in dreadful form, having lost his previous seven matches, but suddenly found his game on the hardcourts to knock out 12th seed Pablo Carreno Busta and number 17 seed Lucas Pouille en route to the last 16.

The first Portuguese player to reach the fourth round at a Grand Slam, the 68th-ranked Sousa never threatened to progress any further as his magical U.S. Open run came to an end.

The biggest concern for sixth-seeded 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 the Serb and his performances suffered under a blazing sun and, with temperatures once again nudging into the 90s Fahrenheit (32 Celsius), the extreme conditions again took a toll on 31-year-old.

He went off court two sets and 2-1 up for a medical evaluation.

"I am not 21 anymore, that was 10 years ago. I still don't feel old but at the same time there is a little biological clock that is not really working in your favour," said Djokovic.

"Heat was the adversity today. I've experienced that in the first round. It's tough.

"It's not easy to play in these kind of conditions. At the same time, you can't do anything but try to be tough and survive, you know, find a way to win."

The 13-times Grand Slam champion made easy work of the opening set, breaking Sousa twice -- the second time to close out the set.

Things got tougher in the second as a sluggish Djokovic laboured before again clinching it with a break.

As temperatures rose so did tempers, with both players engaging in animated arguments with chair umpire James Keothavong over points.

Djokovic, however, was able to keep his cool just long enough to finish off Sousa with another late break.

Cilic topples Goffin

Marin Cilic showed no ill effects from his gruelling, late-night victory two nights ago as the Croatian seventh seed beat David Goffin 7-6(6), 6-2, 6-4 on Monday to reach the US Open quarter-finals.

Former champion Cilic, who rallied back from a two-set deficit to clinch a four-hour, third round match that ended after 2:00 a.m. local time, made a sluggish start against the 10th-seeded Goffin but had enough gas in the tank to advance.

Goffin, who was bidding to become the first Belgian man to reach the U.S. Open quarter-finals, enjoyed a nice start with a break of serve and grabbed a 5-3 edge before moving within two points of taking the first set.

But Cilic suddenly rose to the occasion and deployed his ballistic forehand to get back on serve at 5-5 before securing the opener after an error-filled tiebreak by both players.

From there, the Australian Open runner-up settled into a groove and pulled away from Goffin, who was limited by a sore shoulder and unable to take advantage of an uneven serving display from Cilic.

Cilic broke Goffin in the fifth game of the third set to pull ahead and then held serve the rest of the way before sealing the deal on his third match point with a crosscourt forehand.

The win puts Cilic into the quarter-finals of the year's final Grand Slam for the fifth time.

Next up for Cilic is a 2014 US Open final rematch with Japan's Kei Nishikori, the 21st seed, who beat German Philipp Kohlschreiber 6-3, 6-2, 7-5 earlier on Monday.

Madison Keys eased into the quarter-finals of the US Open with a 6-1, 6-3 victory over Slovakia's Dominika Cibulkova on Monday.

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.

Nishikori advances to quarters

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 of the US Open on another blazingly hot day on Monday.

The Japanese 21st seed, a finalist at Flushing Meadows in 2014 and a semi-finalist in 2016, fired 29 winners to end the run of Kohlschreiber, who had beaten fourth seed Alexander Zverev in the previous round.

Nishikori appeared to be racing towards an easy win before Kohlschreiber unexpectedly broke the 28-year-old to level the third set at 5-5.

But that only delayed the inevitable as Nishikori kept his focus to seal the win and extend his perfect record against the German to 3-0.

"(I was) really lucky to finish in three sets -- it was really hot on the court," a sweat-soaked Nishikori said in an on-court interview. "I think we both struggled a little bit with the heat."

Nishikori will next face either seventh seed Marin Cilic, which will be a rematch of the 2014 final, or Belgian 10th seed David Goffin.