Olympic champion Belinda Bencic came through a punishing match against Iga Swiatek to reach the US Open quarter-finals in humid New York conditions.
The Swiss, 24, won a mammoth first set tie-break to set up a 7-6 (14-12) 6-3 win over the seventh-seeded Pole.
The first set lasted for one hour 24 minutes - which is longer than the entire Adelaide Open final that Swiatek and Bencic contested earlier this year.
She will play Britain's Emma Raducanu or American Shelby Rogers next.
Bencic, who reached the last four at Flushing Meadows in 2019, has yet to drop a set in this year's tournament.
She broke in the first game of the match and served for the set, but Swiatek fought back, garnering a set point of her own before being taken to a tie-break.
The 11th seed then had to fend off another three set points before finally clinching the opener on her fifth attempt.
She acquitted herself better in the second, winning four of the final six games to secure a place in the last eight.
Bianca Andreescu, who beat Bencic here in 2019, faces Greece's Maria Sakkari later on Monday, while Wimbledon finalist Karolina Pliskova takes on Russia's Anastasia Pavlyuchenkova.
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