British number one Katie Boulter suffered a straight-set defeat by world number one Aryna Sabalenka in the second round of the China Open.

Despite serving for both sets at 5-4, world number 56 Boulter lost 7-5 7-6 (7-2) to the Australian Open champion.

Belarusian Sabalenka, US Open runner-up last month, won six successive points in the tie-break.

She will face Italy's Jasmine Paolini for a place in the quarter-finals in Beijing.

"I left everything I had on the court," Sabalenka said. "She played unbelievable tennis. I'm super happy that I was able to win this match."

Poland's Iga Swiatek, replaced as world number one following the US Open, beat France's Varvara Gracheva 6-4 6-1 after a rain delay.

US Open champion and world number three Coco Gauff won 7-5 5-7 7-6 (7-2) against Croatia's Petra Martic, who served for victory at 5-4 in the second set.

"I was just trying to play every ball. She raised her level and was playing really well," said Gauff after extending her winning streak to 14 matches.

"I didn't play my best the whole match, but the tie-breaker was my best. These matches will make me tougher for the rest of the tournament and the rest of the season."

Fellow American Jessica Pegula, the fourth seed, beat Russian Anna Blinkova 6-7 (2-7) 6-2 6-1 to set up a meeting with Latvia's Jelena Ostapenko.

Ukrainian Marta Kostyuk knocked out Wimbledon runner-up Ons Jabeur.

Tunisian seventh seed Jabeur was broken when serving for the first set at 5-4 before world number 33 Kostyuk wrapped up a 7-6 (7-5) 6-1 victory by winning the final five games.

The WTA resumed tournaments in China this year after accepting that the Chinese government will not carry out an investigation into sexual assault allegations made by former player Peng Shuai.