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 yesterday.
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. 
In the women’s section, Madison Keys too eased into the quarter-finals with a 6-1, 6-3 victory over Slovakia’s Dominika Cibulkova yesterday.
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.
On Sunday, six-time champion Serena Williams survived a spirited challenge from unseeded Kaia Kanepi to triumph 6-0, 4-6, 6-3 for her place in the last eight.
The 23-time Grand Slam champion looked set to romp home when she seized the first set from Kanepi in just 18 minutes.
But the hard-hitting Estonian, who took out world number one Simona Halep in the first round, settled down in the second set, shaking off the partisan crowd in a jammed Arthur Ashe Stadium to push Williams the rest of the way.
Williams booked a quarter-final date with Karolina Pliskova, the eighth-seeded Czech who beat Australian Ashleigh Barty 6-4, 6-4. Pliskova defeated Williams in the semi-finals in New York in 2016.
Stephens cruises past Mertens
Defending champion Sloane Stephens, the third seed, eased past Elise Mertens 6-3, 6-3 to book a quarter-final rematch with Latvian Anastasija Sevastova.
Sevastova toppled seventh-seeded Elina Svitolina 6-3, 1-6, 6-0, leaving just two of the top 10 women’s seeds remaining.
Stephens could be headed for a semi-final meeting with Williams, although Williams acknowledged that in Pliskova she’ll face a player with plenty of weapons in addition to her big serve.
“She has a really good forehand. In fact, she doesn’t do a lot of things bad,” Williams said.
Williams heads into the second week at Flushing Meadows tracking two milestones: A seventh US Open title would see her break out of a tie with Chris Evert for the Open Era record and also equal Australian Margaret Court’s all-time record of 24 major titles.
Third seed Juan Martin del Potro crushed Croatia’s Borna Coric 6-4, 6-3, 6-1 on Sunday to set up a quarter-final clash with American John Isner.
The Argentine sent down nine aces and 33 winners to seal a one-sided victory over the 20th seed in just over two hours, with Coric making 30 unforced errors to undermine his own cause.
Next up for Del Potro is 11th seed Isner, who won his second five-setter of the tournament to see off Canada’s Milos Raonic earlier in the day.