Wuhan - Angelique Kerber survived a scare in her first match as world number one before beating Kristina Mladenovic in three sets at the Wuhan Open on Tuesday.
The US and Australian Open champion, who had a bye in the first round, made a convincing start before missing two set points and allowing Mladenovic to take the first set in a tie break.
But the German then swept through the rest of the match, winning 6-7 (4/7), 6-1, 6-4 to set up a third-round meeting with two-time Wimbledon champion Petra Kvitova.
"I was trying to find my rhythm because I was not playing my best in the first set," top seed Kerber said after the match.
Kvitova said she would be trying not to think about Kerber's new status as world number one, formalised when the rankings were updated after this month's US Open, when they play on Wednesday.
"(It) will be for the first time... that I will play her as a number one, which is a little bit different. But I think if I'm on the court, I don't really think about that," she told reporters.
World number four Agnieszka Radwanska also romped into the third round, as last year's US Open finalist Roberta Vinci became the tournament's first seeded casualty.
One-time Wimbledon runner-up Radwanska won 6-4, 6-1 against Russia's Ekaterina Makarova, who bagged Olympic women's doubles gold last month in Rio.
Italy's Vinci, ranked 15, was ousted by Yaroslava Shvedova 7-5, 6-2 - her second defeat at the hands of the Kazakh this year.
Radwanska will next meet an in-form Caroline Wozniacki, who defeated qualifier Kateraina Siniakova 6-4, 6-4 on Tuesday, in the third round of the $2.6 million hardcourt event.
The former world number one beat Poland's Radwanska in the semi-finals of last week's Pan Pacific Open in Tokyo, en route to her first title of the year.
"We always (have) long battles against each other, especially on the slower surface (such) as here," Radwanska said of Wozniacki.
Seven-time Grand Slam champion Venus Williams downed Yulia Putintseva of Kazakhstan 6-3, 6-2, and will next play fellow tour veteran 10th-ranked Svetlana Kuznetsova of Russia. The pair have not met on court since 2009.
American Madison Brengle fell to Kuznetsova 6-0, 6-4 in the second round, as eighth seed Madison Keys beat Caroline Garcia 6-3, 6-4.
Former Wimbledon quarter-finalist Barbora Strycova downed Japan's Misaki Doi, while Daria Kasatkina of Russia beat fellow qualifier American Louisa Chirico.
Results from the third day of the Wuhan Open on Tuesday (x denotes seeding):
Angelique Kerber (GER x1) bt Kristina Mladenovic (FRA) 6-7 (4/7), 6-1, 6-4
Petra Kvitova (CZE x14) bt Elina Svitolina (UKR) 6-3, 6-1
Yaroslava Shvedova (KAZ) bt Roberta Vinci (ITA x13) 7-5, 6-2
Darya Kasatkina (RUS) bt Louisa Chirico (USA) 6-1, 6-1
Svetlana Kuznetsova (RUS x9) bt Madison Brengle (USA) 6-0, 6-4
Agnieszka Radwanska (POL x3) bt Ekaterina Makarova (RUS) 6-4, 6-1
Barbora Strycova (CZE) bt Misaki Doi (JPN) 5-7, 6-0, 6-2
Madison Keys (USA x8) bt Caroline Garcia (FRA) 6-3, 6-4