Aryna Sabalenka of Belarus reacts during the 2nd round of the women's singles match against Katie Boulter of Great Britain in the China Open tennis tournament at the Diamond Court in Beijing, Tuesday, Oct. 3, 2023. Photo: AP
US Open champion Coco Gauff also had to dig deep to get the better of Croatia's Petra Martic in a rollercoaster tie that lasted over three hours.
Sabalenka saved seven break points at 5-5 and then forced the stubborn Briton, ranked 56th in the world, into a rare backhand error to clinch the opening set.
The Belarusian notched another must-win break in the second set to again draw level at 5-5 before triumphing in a tie-break by slamming down an unreturned serve.
She will battle Italy's Jasmine Paolini in the next round for a place in the quarter-finals.
"I think what made the difference was that in the key moments I played a little bit better than her," Sabalenka said at a post-match news conference.
"I think it was all about those last games in each set. She had the opportunity and I'm super glad that I didn't give her those sets easily."
"I kept fighting, kept trying, and that's what made the difference," she said.
Gauff hails 'mental victory'
Martic was serving for the match against Gauff but the world number three fought back to take the game and went on to dominate the ensuing tie-break, winning 7-5, 5-7, 7-6 (7/2).
"Today was a mental victory. I was happy I was able to get through it," said Gauff, who will face Russia's Veronika Kudermetova in her next match.
"I was just telling myself to keep suffering, it will be over in a couple seconds," the 19-year-old said.
"I knew I could outlast her. I just had to be consistent, but also aggressive."
World number two Iga Swiatek eased past France's Varvara Gracheva 6-4, 6-1 to set up a date with fellow Pole Magda Linette.
Fourth-ranked Jessica Pegula bounced back from a set down to beat Russia's Anna Blinkova 6-7 (2/7), 6-2, 6-1.
And France's world number 10 Caroline Garcia suffered a second-set wobble before downing Kazakhstan's Yulia Putintseva 6-3, 3-6, 6-3.
The China Open is taking place for the first time since 2019 after Beijing ditched its isolationist zero-Covid policy.
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