Roger Federer will not be losing any sleep over whether rival Rafael Nadal can match his men’s record of 20 grand slam singles titles, according to his long-term coach Severin Luthi.
Her US Open title defence, and her status as the world number one, have both come to an end for Naomi Osaka.
The reigning champion became the latest big-name casualty of this year’s tournament, crashing out after losing to fellow 22-year-old Belinda Bencic in straight sets.
The Swiss, who reached a career-high ranking of seven in 2016 before a prolonged period of serious injuries saw her drop out of the world’s top 300, broke in the 11th game of the first set to take it 7-5.
Then, at 2-all in the second, a double fault to Osaka saw Bencic break for 3-2 in the second, and she would not surrender the lead for the rest of the match, recording an impressive 7-5, 6-4 victory to move into the last eight at Flushing Meadows for the first time since 2014.
Bencic, a junior Wimbledon champion in 2013, finished with 29 winners, none of which were aces, to just 12 unforced errors. It is also the second time that she has ended the title defence of Osaka in the fourth round, after doing so at Indian Wells in March.
Now with nine top-ten wins this season – more than anyone else – the 22-year-old will face Donna Vekic in the quarter-finals, after the Croat saved a match point to knock out Julia Goerges in three sets.
It will be their second meeting at a major this year after Vekic won their third-round encounter at Roland Garros in May.
For Osaka, the defeat ends a disappointing grand slam calendar, this being the third straight tournament where she has failed to reach the quarter-finals following her triumph at the Australian Open in January.
She will also lose top billing to Ashleigh Barty, who will reclaim top spot in the rankings when they are updated next week, despite the Australian earning no fresh rankings points from her run at Flushing Meadows after repeating her fourth round result from last year.
Barty brushed aside the disappointment of her fourth-round singles exit by teaming up with Victoria Azarenka to thrash the young American pairing of Cori Gauff and Caty McNally 6-0, 6-1 in their third-round doubles match.
They next face top seeds Timea Babos and Kristina Mladenovic in the quarter-finals.
Osaka’s departure also means that there will be a first-time grand slam finalist in the top half of the draw. Of the four women remaining, only Elise Mertens has reached a major semi-final, at last year’s Australian Open.
Mertens booked her place in her first US Open quarter-final by defeating American wildcard Kristie Ahn for the loss of just one game in each set, and now awaits the winner of the match between Taylor Townsend and Bianca Andreescu, which was still to be played.
And of all the women remaining in the draw, only Serena Williams has won a grand slam title, let alone reached a final, and her chances of finally equalling Margaret Court’s record of 24 grand slam singles titles have suddenly multiplied.
On Wednesday morning, she will take on Barty’s fourth-round conqueror, Wang Qiang, while the other bottom half quarter-final will pit Elina Svitolina up against Johanna Konta, with a first US Open semi-final at stake for both players.
In the men’s draw, 24th seed Matteo Berrettini broke new ground, becoming just the third Italian man this decade to reach the quarter-finals of a major, following in the footsteps of Fabio Fognini (2011 French Open) and Marco Cecchinato (2018 French Open).
The 23-year-old put an end to the giant-killing run of Russian Andrey Rublev with a straight-sets win, becoming just the second Italian man in the Open Era to get as far as the quarter-finals at Flushing Meadows, after Corrado Barazzutti in 1977.
His next match will be against French showman Gael Monfils, after he thrashed Spaniard Pablo Andujar in straight sets to advance to his fourth US Open quarter-final, and first since reaching the last four in 2016.
There was disappointment, however, for German sixth seed Alexander Zverev, who remains without a grand slam quarter-final outside of Roland Garros after he lost to Argentine Diego Schwartzman in four sets.
Schwartzman, who also reached the quarter-finals here in 2017 as well as at the French Open that same year, now awaits the winner of the match between Rafael Nadal and Marin Cilic.
The other match still to be played at the time of writing is between American wildcard Taylor Townsend and Canadian 15th seed Bianca Andreescu, who won the Rogers Cup in Toronto last month.
The first of the quarter-finals gets underway on Wednesday morning, with Roger Federer and Stan Wawrinka looking to set up an all-Swiss semi-final when they face off against Grigor Dimitrov and Daniil Medvedev in their respective matches.
On the women’s side, Serena Williams will start a red-hot favourite to progress to the semi-final, where she would await the winner of the clash between Elina Svitolina and Johanna Konta.
Arthur Ashe Stadium
Day session – play starts at 12.00pm (2.00am AEST)
 Elina Svitolina (UKR) vs  Johanna Konta (GBR)
 Stan Wawrinka (SUI) vs  Daniil Medvedev (RUS)
Night session – play starts at 7.00pm (9.00am AEST)
 Serena Williams (USA) vs  Qiang Wang (CHN)
 Roger Federer (SUI) vs Grigor Dimitrov (BUL)