NEW YORK (CBSNewYork/AP) -- Venus Williams failed to convert a match point Monday and lost in the fourth round of the US Open to a player a dozen years younger than her, 10th-seeded Karolina Pliskova of the Czech Republic.
Pliskova reached the first Grand Slam quarterfinal of her career by coming back to edge the seven-time major champion 4-6, 6-4, 7-6 (3) at Arthur Ashe Stadium.
The 24-year-old Pliskova had never been past the third round in 17 previous appearances at majors.
At 36, Williams, the sixth seed, was trying to become the oldest Grand Slam quarterfinalist since Martina Navratilova was 37 at Wimbledon in 1994.
Earlier Monday, Simona Halep reached the quarterfinals for the second straight year, beating Carla Suarez Navarro in straight sets.
The fifth-seeded Romanian won 6-2, 7-5. She could face No. 1 Serena Williams next. The 22-time major champ plays Yaroslava Shvedova later in the day.
Suarez Navarro, seeded 11th, was seeking the sixth Grand Slam quarterfinal of her career.
Halep had a chance to serve out the match at 5-4 in the second set but got broken. She then broke Suarez Navarro's serve in the next game and successfully served it out in her second opportunity.
On the men's side, Juan Martin del Potro is back in the quarterfinals after Dominic Thiem retired in the second set of their match.
The eighth-seeded Thiem took a medical timeout to have trainers look at his right knee after the set's fifth game. He returned to the court for one point before deciding he couldn't go on.
Del Potro had won the first set 6-3 and was up a break in the second.
Thiem, who turned 23 on Saturday, has had a breakthrough year, reaching the French Open semifinals and cracking the top 10. But the long season was starting to wear on his body.
Del Potro knows all about that. The 2009 US Open champ missed the tournament the last two years after surgeries on his left wrist.
But his stunning run to the Olympic silver medal signaled he's a contender again.
Del Potro got a huge break Monday when he spent only 72 minutes on court. He's played just 10-plus sets through four rounds.
At No. 142, del Potro is the lowest-ranked US Open quarterfinalist since Jimmy Connors in 1991.
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