Danielle Collins of the U.S. reacts after winning a point against Elise Mertens of Belgium during their fourth round match at the Australian Open tennis championships in Melbourne, Australia, Monday, Jan. 24, 2022. AP
It was the first time Collins has rallied from a set down to win back-to-back matches at a Grand Slam tournament.
The 28-year-old American also dropped the first set in her third-round win over Clara Tauson.
The No. 27 seed was a semifinalist at the 2019 Australian Open, which remains her best run at a major.
A win over either two-time major winner Simona Halep or French veteran Alize Cornet in the next round would get Collins back into the last four.
``Today it was really physically tough for me,'' Collins said. ``I played a long match the other day _ 2 1/2 hours _ and then I played doubles, so I spent about five hours on court.
``I had to make a lot of technical adjustments to make myself comfortable moving around, especially serving.``
Collins was aggressive with her ground strokes, hitting 45 winners and and making 41 errors against Mertens. She converted five of her 18 break-point chances and clinched the victory when Mertens, a semifinalist in Australia in 2018, served a double-fault.
In fourth-round men's matches later Monday, U.S. Open champion Daniil Medvedev was playing Maxime Cressy, fourth-seeded Stefanos Tsitsipas was scheduled to play No. 20 Taylor Fritz and 2014 U.S. Open champion Marin Cilic was against ninth-seeded Felix Auger-Aliassime.
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