It was business as usual for the men at the U.S. Open but manic Monday on the women's side with the draw blown wide open by upsets that saw contenders Ons Jabeur and Jessica Pegula join defending champion Iga Swiatek heading through the exit doors.

World number one and defending champion Carlos Alcaraz began the second week of the season's final Grand Slam flashing a big smile and superb form as he eased past Italian Matteo Arnaldi 6-3 6-3 6-4 and into the last eight.

The Spaniard was joined by third seed and 2021 winner Daniil Medvedev, eighth seed Andrey Rublev and 12th seed Alexander Zverev.

"I think the intensity from the beginning until the last ball, I played a really solid match," said Alcaraz, who is bidding to become first the man to successfully defend his U.S. Open crown since Roger Federer in 2008.

While the men kept pretty much to the form book the women's was in the shredder, the trophy chase turned on its head by 24 hours of stunning results that started on Sunday evening with Swiatek falling 3-6 6-3 6-1 to Jelena Ostapenko.

When play resumed on Monday so did the upsets.

The first match on Arthur Ashe saw U.S. third seed Jessica Pegula swept aside by compatriot and 2017 finalist Madison Keys before Tunisia's 'Minister of Happiness' Jabeur was left a forlorn figure after falling 6-2 6-4 to China's Zheng Qinwen.

Jabeur had returned to Flushing Meadows bidding to become the first Arab and African woman to win a major and claim the Grand Slam title that was denied her at the last two Wimbledon finals and last year's U.S. Open.

But a respiratory illness has left her struggling to catch her breath, saying she felt like a "zombie" at times in the tournament, but bravely battled before simply running out of puff.

Second seed Aryna Sabalenka restored some order at the end of the day with a clinical 6-1 6-3 win over Russian 13th seed Daria Kasatkina.

Sabalenka, who will bump Swiatek from top spot in the rankings when they are updated on Sept. 11, played like a world number one, needing only 28 minutes to wrap up the opening set and strolling off Arthur Ashe to applause in just over an hour.

Earlier in the day on Louis Armstrong, Peyton Stearns of the United States looked set to deliver another shock when she took the opening set from Wimbledon champion Marketa Vondrousova but the ninth seeded Czech recovered to register a 6-7(3) 6-3 6-2 win.

Russians Medvedev and Rublev both moved on with workmanlike four-set wins.

After two late-night matches Medvedev finally finished work 'early' on Monday, beating Australian Alex de Minaur 2-6 6-4 6-1 6-2 while Rublev dispatched the last Briton, Jack Draper, 6-3 3-6 6-3 6-4.

The wins set up a fascinating showdown between the two friends, Rublev the godfather to Medvedev's daughter.

The last match on Arthur Ashe featured sixth-seeded Italian Jannik Sinner and 12th seeded German Alexander Zverev, which became the late-night thriller everyone had been predicting.

Played in sweltering conditions, the nearly five-hour marathon turned into a battle of wills as well as skills, with both players battling cramp as well as each other.

In the end it was Zverev, the 2020 finalist, who was able to dig just a little bit deeper to claim a 6-4 3-6 6-2 4-6 6-3 win.

The match was also interrupted when Zverev demanded a spectator be removed, the German telling the umpire that the fan had yelled "the most famous Hitler phrase".

After identifying the man security removed him from the stadium.

(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Ken Ferris, Peter Rutherford)