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.