A summary of Monday's action at the US Open.
Frances Tiafoe played the match of his life to beat second seed Rafael Nadal 6-4, 4-6, 6-4, 6-3 and reach the quarter-finals of the US Open on Monday.
It was the first time this year that Nadal, who had been chasing a record-extending 23rd Grand Slam title, was been beaten in a major.
The American covered his face with his hands as he soaked up the cheers from a packed house at Arthur Ashe Stadium after breaking Nadal for a fifth time to claim the biggest upset of the tournament.
"I don't even know what to say right now, I'm beyond happy, I'm almost in tears," Tiafoe said in an on-court interview.
"I can't believe it. He is definitely one of the greatest of all time. I played unbelievable tennis today but I really don’t know what happened."
While Tiafoe did indeed play sublime tennis, he also benefited from an uncharacteristically poor serving and returning performance from Nadal. The Spaniard produced nine double faults and hit just 33 winners to Tiafoe's 48.
With the win, Tiafoe snapped Nadal's streak of 17 straight majors where he reached the quarter-finals or better. The Spaniard had triumphed at the Australian and French Opens this year before withdrawing with an abdominal injury before his semi-final at Wimbledon.
Next up for Tiafoe is a quarter-final showdown with Russian Andrey Rublev, who defeated Briton Cameron Norrie 6-4, 6-4, 6-4 earlier in the day.
Swiatek survives surprise test from Niemeier
Iga Swiatek was given a mighty scare by little-known Jule Niemeier on Monday before the Polish top seed finally handed the 108th-ranked German a 2-6, 6-4, 6-0 reality check in the fourth round.
Swiatek, who collected her second Roland Garros title amid a 37-match winning streak earlier this year, barely looked like the world's best player as she sprayed the court with errors to surrender the opening set.
She handed Niemeier a break in the third game of the second set with a clumsy mistake at the net. Sitting on her bench with her towel over her head during the changeover, she loudly smacked her thigh in anger before returning to the court with new resolve, winning the next three games.
The pair traded breaks twice to close out the second set but Niemeier scarcely put up a fight in the third, producing 14 unforced errors as her game quickly unravelled.
Swiatek, who won in Doha, Indian Wells, Miami and Rome this year, sounded rattled after the match as her usual legion of Polish supporters rallied around her from the stands.
"I'm just proud that I didn't lose hope," she said in an on-court interview. "I had hard time like pushing her back."
It is the first time she has reached the quarter-finals at Flushing Meadows. She next faces in-form American Jessica Pegula.
"I'm really happy to play in front of you guys and I hope my matches are going to be good to watch so you're not going to waste your time here," she said.
Alcaraz beats Cilic in late-night thriller to set up Sinner clash
Spaniard Carlos Alcaraz beat 2014 champion Marin Cilic 6-4, 3-6, 6-4, 4-6, 6-3 to set up a next generation quarter-final clash against Jannik Sinner.
After battling for three hours and 53 minutes at Arthur Ashe Stadium, where the roof was closed due to rain, Alcaraz, 19, dropped to his knees in jubilation after sealing the contest on his first match point when Cilic's return hit the net.
The sizeable crowd on the main showcourt gave the players a standing ovation with the clock striking 2.24 a.m., a couple of minutes short of the latest ever finish at the New York Grand Slam.
Alcaraz's victory over the 15th-seeded Croatian ensured there will be a new men's Grand Slam champion on Sunday and also kept the Spaniard in contention to become the youngest world number one when the ATP rankings are updated after the final.
The third seed will next meet 21-year-old Italian Sinner, seeded 11th, for a maiden Grand Slam semi-final spot.
Sabalenka overcomes crowd and Collins to reach quarters
Aryna Sabalenka overcame a partisan New York crowd and an in-form Danielle Collins to secure a 3-6, 6-3, 6-2 win on Monday and set up a quarter-final against familiar foe Karolina Pliskova.
American Collins came out firing to take the first set but the tide turned in the second when sixth seed Sabalenka won a marathon service game to lead 4-3.
Sabalenka rolled on from there, breaking Collins in the next game and capturing the set with her fifth ace.
She broke again early in the deciding third set and raised her arms in triumph when Collins' service return landed in the net on match point.
Sabalenka, a semi-finalist at Flushing Meadows last year, improved to 4-0 against 19th seed Collins.
"I just love the court, I love the crowd," she said at Arthur Ashe Stadium.
"Even if you guys support her, which is expected, I love this place and I want to play here as much as I can."
Sabalenka is battle tested going into the quarter-finals.
She clawed her way back from a set and 5-1 down against Kaia Kanepi in the second round, saving two match points in the process.
"When you come back from that kind of score you know that nothing can hurt you," she said.
"You go into the next match and know that you will fight for it no matter what."
Next up for Sabalenka is big-serving Czech Pliskova, who won a gritty three-setter over Victoria Azarenka, also of Belarus, earlier in the day.
Sabalenka and the tournament's 2016 finalist Pliskova have split their four head-to-head meetings 2-2.
Sabalenka said maintaining her composure if the match is not breaking her way will be key to victory.
"Right now I really expect great level from her," she added.
"It's going to be tough. It's a tough fight."
Rublev whips Norrie
Rainy weather could not dampen Russian Andrey Rublev's sublime form as he rolled past Briton Cameron Norrie 6-4, 6-4, 6-4 to reach the US Open quarter-finals for the third time.
The ninth seed sent over 11 aces and had fewer than half the unforced errors his opponent did in a brisk affair that was surely a reprieve after Rublev endured two five-set battles in the earlier rounds.
With 24-year-old Rublev up a break in the second set, rain forced a considerable delay as Louis Armstrong Stadium's retractable roof slowly slid into place and workers mopped up the court before the eighth game.
Roland-Garros quarter-finalist Rublev was unfazed, dropping only two of his first serve points in the third set and getting the critical break over the seventh seed in the ninth game with an exquisitely placed backhand winner.
On the hunt for a maiden major title, Rublev's recent hard court performances painted an inconsistent picture, as he crashed out of his Montreal opener to Briton Dan Evans and lost in the third round at Cincinnati.
But he appeared to be fully in command of his game on New York's famed blue courts on Monday, with either American Frances Tiafoe or Spanish second seed Rafa Nadal waiting in the next round.
"I played a good match," Rublev said in an on-court interview.
"This is the US Open, this is a Grand Slam, everyone is nervous, everyone is tight."
Sinner survives Ivashka scare
Jannik Sinner rallied from 3-1 down in the fifth set to beat Ilya Ivashka 6-1, 5-7, 6-2, 4-6, 6-3 and reach the quarter-finals.
Sinner's sublime drop-shot winner broke world No. 73 Ivashka for a 4-3 lead in the decider and the Italian went on to seal the victory when the Belarusian's forehand sailed long on match point.
Sinner, seeded 11th, said the crowd at Louis Armstrong Stadium had helped get him across the finish line.
"The atmosphere is always very great, especially when I'm down," he said in an on-court interview.
"Thanks to you guys for keeping my head up because today I was struggling. I was not playing my best and in the fifth set I tried to dig deep.
"I'm very happy to be in the next round."
The 21-year-old has now reached the quarter-finals of all four Grand Slam tournaments, becoming the youngest man to do so since Novak Djokovic in 2007-08.
Ivashka, 28, exits with his head high after impressive wins over Sam Querrey, eight seed Hubert Hurkacz and Sinner's countryman Lorenzo Musetti for his deepest run in New York.
Pegula shines through rain to beat Kvitova
A surprise shower failed to stop American Jessica Pegula from reaching her third Grand Slam quarter-final this year as she toppled twice Wimbledon champion Petra Kvitova 6-3, 6-2.
One of the most reliable returners in the sport, Czech Kvitova had won both of their previous meetings but was left to rue her missed chances -- as she converted only two of the six break points she earned.
Rain forced a 44-minute stoppage early on in the match, with tournament staff scrambling to close the retractable roof on Ashe and mop up the court.
But eighth seed Pegula was unfazed as she broke Kvitova to love in the seventh and ninth games to close out the first set.
Even when Kvitova took a 2-0 lead in the second, Pegula kept her nerve to storm back and win the next six games to wrap up the win.
"I just told myself not to get frustrated," Pegula said after she joined fellow American Coco Gauff in the last eight. "I just really wanted to stay committed to hitting my spots.
"It feels amazing - I'm so happy. I thought I handled my nerves and stuff really well."