Bianca Andreescu became the first teenager to reach the U.S. Open semifinals in a decade, beating Elise Mertens 3-6, 6-2, 6-3.
The No. 15 seed improved to 13-3 in three-set matches and 31-4 overall with two titles this season.
The 19-year-old Canadian became the youngest semifinalist at Flushing Meadows since Caroline Wozniacki was also 19 when she was the runner-up in 2009.
The 25th-seeded Mertens was bidding for her second major semifinal, having lost in that round at the Australian Open in 2018.
Matteo Berrettini of Italy advanced to his first Grand Slam semifinal after nearly four exhausting hours, edging Gael Monfils 3-6, 6-3, 6-2, 3-6, 7-6 (5).
With both players fighting fatigue and a faulty serve down the stretch, Berrettini finally closed it out on his fifth match point — after double-faulting away his first chance long before that.
The match that began under muggy conditions ended under the closed roof at Arthur Ashe Stadium, 3 hours, 57 minutes after it began.
The 24th-seeded Berrettini advanced to face No. 2 Rafael Nadal or No. 20 Diego Schwartzman.
Belinda Bencic powered her way into her first Grand Slam semifinal, wearing down Donna Vekic for a 7-6 (5), 6-3 victory at the U.S. Open.
The No. 12 seed from Switzerland followed up her victory over No. 1 Naomi Osaka in the fourth round by taking control of the match midway through the second set and winning the final three games.
Five years after making her lone quarterfinal appearance in a major tournament at the U.S. Open, Bencic advanced to face Andreescu.
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