Rafael Nadal ramped up his quest for a fourth US Open title with an impressive win over 2014 champion Marin Cilic to advance to the quarter-finals.
Second seed Nadal the winner at Flushing Meadows in 2010, 2013 and 2017 — produced some electrifying moments of brilliance to end the challenge of Croatian 22nd seed Cilic 6-3, 3-6, 6-1, 6-2.
Osaka ousted by 13th seed Bencic
Reigning champion Naomi Osaka was knocked out of the US Open by Swiss 13th seed Belinda Bencic 7-5, 6-4 in the last 16.
Bencic defeated Osaka for the third time in as many meetings this year and will play Croatian 23rd seed Donna Vekic in the quarter-finals.
Osaka will lose the number one ranking to Ashleigh Barty as a result of the loss.
Zverev eliminated by Schwartzman
Alexander Zverev slumped to a four-set defeat. The German was enjoying his deepest run in New York but committed 17 double faults and 65 unforced errors and received a point penalty for swearing as Schwartzman advanced to a second US Open quarter-final in three years.
"Generally my season so far has not been the best," said Zverev, who has reached just two quarter-finals in 18 Grand Slam appearances.
Vekic saves match point, advances
Croatian Donna Vekic, the 23rd seed, saved a match point in the second set and made her first Slam quarter-final by rallying past German 26th seed Julia Goerges 6-7 (5/7), 7-5, 6-3.
"I don't even know how I won this match," Vekic said. "She was serving for the match. She had match point. I just kept fighting and believing I could win. It feels pretty amazing."
Monfils to face Berrettini
Matteo Berrettini became just the second Italian man to progress to the US Open quarter-finals, 42 years after Corrado Barazzutti's run to the last four in New York.
Berrettini, the 24th seed, eased to a 6-1, 6-4, 7-6 (8/6) win over Russia's 43rd-ranked Andrey Rublev to reach the last eight at a Grand Slam for the first time.
"It's something really crazy. I cannot believe it right now. I need a few hours to understand what happened," said Berrettini, 23, who goes on to play French 13th seed Gael Monfils.
Monfils, a 2016 US Open semi-finalist, crushed the 33-year-old Andujar's bid to become the oldest player in the Open era to reach his first Grand Slam singles quarter-final with a 6-1, 6-2, 6-2 rout.
Record US Open crowds
This year's US Open has set an attendance record through the US Labor Day Holiday weekend, with 540,333 people at the tournament, the highest attendance for any US Open through the first eight days, eclipsing last year's mark of 538,266.
The event is on pace to break the total attendance mark of 732,663 set last year, when the new Louis Armstrong Stadium opened.
Tiger cheers on Nadal
Among those in the crowd watching Nadal was reigning Masters champion Tiger Woods, the golf legend who underwent spinal fusion surgery but fought back to win his 15th major title this year at Augusta National. "Playing in front of Tiger is a very special thing," Nadal said.
"I never had big idols but if I have to say one idol it's him. It's a big pleasure to have him here supporting me. I want to congratulate him on one of the most amazing comebacks in sports this year."
As for Nadal's golf swing matching his amazing tennis racquet swing, well... "It's much better if Tiger don't see my swing. Maybe he can lose a little bit the rhythm after that."
It was 48 years ago today...
Monday marked the 48th anniversary of the first US Open singles wins for the all-time record holders in US Open singles matches wins, Jimmy Connors and Chris Evert.
Playing on his 19th birthday, Connors beat Alex Olmedo 2-6, 5-7, 6-4, 7-5, 7-5 in the first of his men's record 98 US Open triumphs. Evert, 16, downed Edda Buding 6-1, 6-0 in 42 minutes for the first of her record 101 US Open wins.
Serena Williams will try for her 100th US Open victory on Tuesday against China's Wang Qiang. Williams would match Evert's mark with a semi-final win and break it if she can capture her seventh US Open title.
'The sarcasm is beautiful'
Naomi Osaka wasn't sure why fans were booing Daniil Medvedev but she liked the way the Russian fifth seed was sarcastically praising crowds after his victories.
Fans began booing him after he was caught on camera making an obscene gesture and he followed up by praising critics for providing extra motivation, which delighted Osaka, who said, "The sarcasm is beautiful."
"I don't know why they're booing him," she said. "But it's just so funny. Like every day, he has something new to say."