American 11th seed John Isner’s hopes of surpassing his best finish at a US Open could be cut short if his first baby arrives sooner than expected.

Isner reached the quarter-finals with a 3-6 6-3 6-4 3-6 6-2 win over Canadian 25th seed Milos Raonic on Sunday to equal his best showing here.

His first child is due on 22 September but he has already been thinking what would happen if there was a clash.

“I would play if it worked out I could get there and get back,” he said.

He added in comments reported on the US Open website: “If it was the day of the match, not possible. I’m not going to miss the birth, but we’ll see.”

Wimbledon semi-finalist Isner will face Juan Martin del Potro or Borna Coric next after reaching the last eight in New York for the first time since 2011.

He is the only American remaining in the men’s draw after 18th seed Jack Sock was knocked out by Georgian Nikoloz Basilashvili in the second round.

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Elsewhere, ninth seed Dominic Thiem also reached the quarter-finals by beating 2017 runner-up Kevin Anderson 7-5 6-2 7-6 (7-2) of South Africa.

The Austrian broke late in the first set and twice in the second before winning the third in a tie-break on Arthur Ashe Stadium..

It is the first time Thiem has reached the last eight in New York, and he will face 17-time Grand Slam winner and defending champion Rafael Nadal.

French Open finalist Thiem called the win “one of his best matches ever”.

Twelve months ago the 24-year-old had two match points in the fourth round against Del Potro but lost in five sets.

“It’s a dream coming true,” said Thiem. “I was really close last year, but I couldn’t close it out.”

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Former champions Novak Djokovic and Roger Federer will set up a mouth-watering US Open quarter-final if they win their matches on Monday.

Sixth seed Djokovic faces Portuguese Joao Sousa in the fourth round, while Federer plays Australian John Millman.

The former world number ones have not faced each other so early in a Grand Slam since 2007, when Federer won to reach the Australian Open last eight.

First Djokovic must beat Sousa, making his debut at this stage of a Slam.

The world number 44 has already knocked out two seeds – Frenchman Lucas Pouille in the third round and Spain’s Pablo Carreno Busta in the second.

“He’s a fighter, he’s a grinder,” Djokovic said. “He will not hand you the victory, you’ve got to earn it.”

Federer’s opponent Millman, the world number 52, is also competing in unknown territory after knocking out 14th seed Fabio Fognini in the second round.

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Sharapova enjoying the nights

Also competing on Arthur Ashe Stadium is Russian 22nd seed Maria Sharapova, who is up against Spanish 30th seed Carla Suarez Navarro in the fourth round.

The five-time Grand Slam champion is looking to extend her perfect record of 23 wins in the night session at Flushing Meadows.

The 2006 US Open winner reached the quarter-finals of the French Open earlier this year but has not gone beyond the fourth round in New York since 2012.

“It’s the energy you get, no doubt I feed off this energy,” Sharapova, 31, said.

“I don’t remember how old I was when I played my first night match, but I’m sure I was young enough to still be intimidated by the city and the lights and the atmosphere, the noise.

“But I really turned that around. I think I thrive on that. I love the atmosphere. I love that they know how to cheer hard. I thrive on playing under the lights for some reason. I love that.”

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Also in action…

Last year’s runner-up Madison Keys faces Slovakian 29th seed Dominika Cibulkova on Arthur Ashe before Djokovic’s match with Sousa.

Japanese 21st seed Kei Nishikori takes on German Philipp Kohlschreiber on Louis Armstrong, before compatriot Naomi Osaka faces 26th seed Aryna Sabalenka of Belarus.

And seventh seed Marin Cilic, the 2014 champion, is up against Belgian 10th seed David Goffin in the last match of the evening.

Czech eighth seed Karolina Pliskova saved eight break points to beat Ashleigh Barty in straight sets and reach the US Open quarter-finals.

The 2016 finalist broke in the opening game of the first set and the third game of the second to win 6-4 6-4.

But she withstood plenty of pressure from the Australian 18th seed.

Pliskova will face either American 23-time Grand Slam champion Serena Williams or unseeded Estonian Kaia Kanepi for a place in the last four.

“It was very tough even though the score looks easy,” Pliskova said. “I’m very happy to be through.”

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Novak Djokovic stayed on course for a quarter-final meeting with Roger Federer after beating France’s Richard Gasquet in straight sets to move into the US Open last 16.

Sixth seed Djokovic, US Open champion 2011 and 2015, won 6-2 6-3 6-3 on Arthur Ashe Stadium.

It was his 13th victory over Gasquet in 14 career meetings.

“It was a great match from the beginning to the end,” said Djokovic, who will next face unseeded Joao Sousa.

If he beats the Portuguese, the world number six could face second seed Federer in the quarter-finals. The Swiss takes on Australia’s John Millman in his fourth-round match.

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Djokovic cruised through the first two sets against Gasquet, 32, but had to fight off two break points when 3-2 up in the third.

He let out a roar after coming out on top in a rally that had the stands rocking.

“Obviously in the third set Richard raised his level. The crowd was amazing toward the end of the match, it was a real night session match here at the US Open,” added the Serb.

Portuguese Sousa upset 17th seed Lucas Pouille of France 7-6 (7-5) 4-6 7-6 (7-4) 7-6 (7-5).

“He’s a fighter, he’s a grinder,” Djokovic said of Sousa. “He will not hand you the victory, you’ve got to earn it.”

Former champion Marin Cilic reached the fourth round after a tough match against 19-year-old Australian Alex De Minaur that finished at 2:22am local time – one of the latest finishes in the history of the US Open.

The Croat clinched a 4-6 3-6 6-3 6-4 7-5 victory on his eighth match point against De Minaur, who has risen rapidly this season.

Cilic praised his opponent’s “incredible fighting spirit”.

“He was fighting his heart out and it was just an insane match,” added Cilic. “He played some amazing tennis and really a couple of points were taking him away from the victory. I was just a little bit luckier today.”

The match was just four minutes short of the record for the latest finish of 2.26am, which has happened on three occasions – between Mats Wilander and Mikael Pernfors in 1993, Philipp Kohlschreiber and John Isner in 2012 and Kei Nishikori and Milos Raonic in 2014.

Cilic will face 10th seed David Goffin on Monday.

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Angelique Kerber and Petra Kvitova were both knocked out of the US Open on Saturday, leaving defending champion Sloane Stephens as the sole remaining top-six seed in the women’s draw.

Wimbledon champion Kerber was beaten 3-6 6-3 6-3 by Slovak 29th seed Dominika Cibulkova in the third round.

Two-time quarter-finalist Kvitova lost 7-5 6-1 to in-form Belarusian Aryna Sabalenka.

None of this year’s Grand Slam winners are now left in the women’s singles.

French Open champion Simona Halep was knocked out by Kaia Kanepi in the first round, while Australian Open champion Caroline Wozniacki experienced a shock second-round loss to Ukraine’s Lesia Tsurenko.

• Sharapova beats Ostapenko to reach fourth round
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Kerber broke three times in the first set but Cibulkova repeated the feat in the second to take it to a decider.

The German fourth seed, 30, was then broken again twice in the final set and misses out on a last-16 tie with last year’s finalist Madison Keys.

American 14th seed Keys, runner-up to Stephens last year, recovered from a set down to reach the last 16, beating Serbia’s Aleksandra Krunic 4-6 6-1 6-2.

Keys, 23, was broken in her first service game of the match en route to losing the first set but broke twice in the second set to take it to a decider.

The first five games of the third set went against serve before the American held for 4-2 and closed out the match.

“I was definitely a little bit nervous and she came out playing really well and put pressure on me from the start. I am just happy to be in the next round,” Keys, 23, said.

“There were too many unforced errors in the first set but I’m glad I settled down a bit and played much better. I wasn’t aggressive enough in the first set and was too passive. The biggest thing was trusting myself.”

Battle of the 20-year-olds in the fourth round

Sabalenka warmed up for Flushing Meadows with a first career title at New Haven and came into the tournament at a career-high world ranking of 20th.

The 26th seed hit 21 winners to defeat Czech fifth seed Kvitova, 28, and will face fellow 20-year-old Naomi Osaka, for a quarter-final spot after the Japanese 20th seed thrashed Belarusian Aliaksandra Sasnovich 6-0 6-0.

“I really like to play on the big stages,” Sabalenka said. “I really like to feel the support of the people. I didn’t expect anything, I just went on the court and tried for every point and now I’m so happy.”

Kvitova’s exit also means just three of the top 10 women’s seeds made it into the fourth round, with Ukraine’s Elina Svitolina (seeded seventh) and Czech Karolina Pliskova, the eighth seed, both through.

Another high-ranked departure was French sixth seed Caroline Garcia, conqueror of Britain’s Johanna Konta in round one, who lost 5-7 6-4 7-6 (7-4) to Carla Suarez-Navarro.

After taking the first set, Garcia was broken in the opening game of the second set and could not find a way back, before losing a tight third set on a tie-break.

Spanish 30th seed Suarez-Navarro will face Russian former champion Maria Sharapova after she beat Latvian 10th seed Jelena Ostapenko 6-3 6-2.

Elsewhere, Dutch 13th seed Kiki Bertens was knocked out by Czech Marketa Vondrousova 7-6 (7-4) 2-6 7-6 (7-1).