British No 1 Katie Boulter was knocked out of the China Open by American Coco Gauff in straight sets 7-5 6-2.
A battling performance saw Boulter test the world No 6, but Gauff managed to snatch a tight first set before wrapping up victory in the second to win comfortably.
Gauff will now face either four-time Grand Slam champion Naomi Osaka or fellow American Katie Volynets in the last 16.
Boulter beat Taylor Townsend to set up a meeting with former US Open champion Gauff and there was little to separate the pair in the early stages, but after breaking Boulter's serve in the sixth game Gauff began to pull ahead.
However, the British No 1 battled back and some solid serving helped her recover from 5-2 down to level at 5-5 before Gauff eventually took the first set on her third set point of the 12th game.
Gauff enjoyed a bright start to the second set and broke Boulter in the fourth game to move ahead before going on to claim victory on her second match point.
Third-ranked Jessica Pegula responded to losing a marathon first set to rally for a 6-7 (9-11) 6-1 6-2 win over Veronika Kudermetova in the third round.
Pegula has won 17 of her last 19 matches, including defending her title in Toronto and making finals at Cincinnati and the US Open. Her only defeats have come to Aryna Sabalenka, the top-seeded player in Beijing.
"Every time I've played her, it's always been really tough," Pegula said. "After I came back from 2-5 in the first set, I kind of knew what to do, I just had to execute in the next couple sets. I'm happy I was able to kind of figure that out and finally help my head-to-head against her."
The American made three service breaks in the first set, but also lost three of her own, with Kudermetova prevailing in a lung-busting 20-point tie-break to take the lead.
The loss of the tie-break seemed to spur Pegula to life as she found her groundstroke range to break her Russian opponent's serve twice in each set to take the match in just over two-and-a-half hours. It was Pegula's first win against the 39th-ranked Kudermetova in three attempts.
Pegula will play the 15th-seeded Paola Badosa in the fourth round after the Spaniard beat Serbian Rebecca Sramkova 7-5 7-5.
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What's coming up on Sky Sports Tennis in October?
- Shanghai Masters - ATP 1000 (October 2-13 - Jack Draper in action)
- Wuhan Open - WTA 1000 (October 6-12 - Emma Raducanu in action)
- Almaty Open, Kazakhstan - ATP 250 (October 14-20)
- Stockholm Open, Sweden - ATP 250 (October 14-20)
- European Open, Antwerp - ATP 250 (October 14-20)
- Japan Open, Osaka - WTA 250 (October 14-20)
- Ningbo Open, China - WTA 500 (October 14-20)
- Erste Bank Open, Vienna - ATP 500 (October 21-27)
- Swiss Indoors, Basel - ATP 500 (October 21-27)
- Guangzhou Open, China - WTA 250 (October 21-27)
- Toray Pan Pacific Open Tennis, Tokyo - WTA 500 (October 21-27)
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