Williams, chasing a record-equalling 24th Grand Slam title, came from a set down to oust 2017 champion Sloane Stephens 2-6, 6-2, 6-2, in what she called an “intense” encounter on Arthur Ashe Stadium.
“In that first set I don’t think she made any errors, honestly. She was just playing so clean and I just said, ‘I don’t want to lose in straight sets,'” said Williams.
With spectators barred from this year’s Flushing Meadows event due to the pandemic, second and fourth seeds Sofia Kenin and Naomi Osaka took advantage of suites they have been assigned to check out the competition.
“It’s cool us players can watch each other. It’s interesting, I like it,” said Williams, who will play 15th seed Maria Sakkari for a place in the quarter-finals.
The Greek player, who stunned Williams at the Western & Southern Open last month, progressed with a 6-3, 6-1 dismantling of America’s 22nd seed Amanda Anisimova.
Off the court, number one seeds Kristina Mladenovic and Timea Babos were yanked from the women’s doubles competition after Mladenovic was instructed to quarantine for coming in contact with Benoit Paire, who tested positive for COVID-19 last weekend.
“All persons who were identified as having prolonged close contact with the infected player will quarantine in their rooms for the remainder of their quarantine period,” the United States Tennis Association said in a statement.
The USTA said that local public health issues had issued the quarantine notices, which prevented the players commuting from their hotel to the USTA Billie Jean King National Tennis Center.
“The USTA is obligated to adhere to government guidance at the State, City and County level,” the body said.
The shock intervention came a day after health officials tried to prevent Adrian Mannarino, who had also been in contact with Paire, from playing his last-32 match.
Officials from New York state’s department had contacted the USTA to say that Mannarino should have been quarantining in his hotel room.
The match got underway three hours after its scheduled start time, after authorities ruled it could go ahead following discussions with tennis officials that also included lobbying by world number one Novak Djokovic.
Mannarino and Mladenovic were two of 11, mostly French players, put under enhanced safety protocols on Monday after Paire was withdrawn from the US Open on Sunday following his positive test coronavirus.
The players signed an agreement with New York City authorities that allowed them to remain in the tournament under the enhanced restrictions, which involved daily testing and barred them from communal areas in their hotel.
Mannarino told reporters Friday that organizers told him that New York state authorities had taken over case from the city and ruled that he was now not allowed to play.
Following her first-round singles win on Monday, Mladenovic said she had been “living in a nightmare” following Paire’s positive test result.
The US Open is taking place behind closed doors because of the deadly pandemic.
Players movements are tightly controlled and everyone onsite is being tested regularly to minimize the risk of infection.
Paire, who later tested negative, exited the tournament in a huff, accusing authorities of operating a “fake bubble.”
The players who were in contact with him have been told they won’t be allowed to fly out of New York until next week.
Back on the court Saturday, Russian third seed Daniil Medvedev, Italy’s sixth seed Matteo Berrettini and Andrey Rublev, all enjoyed easy three-set wins.
Elsewhere, Canada’s Vasek Pospisil, ranked 94th in the world, shocked eighth-seeded Spaniard Roberto Bautista Agut, 7-5, 2-6, 4-6, 6-3, 6-2 and Australia’s 21st seed Alex de Minaur upset 11th-seeded Russian Karen Khachanov 6-4, 0-6, 4-6, 6-3, 6-1.
In the women’s draw, unranked Bulgarian Tsvetana Pironkova caused her second upset of the week, knocking out 18th seed Donna Vekic in straight sets.
Pironkova, playing her first tournament in three years after having a child, stunned 10th seed Garbine Muguruza in round two.