WUHAN, China -- Second-ranked Caroline Wozniacki reached the third round of a tournament for the first time since June at the Wuhan Open on Tuesday, while No. 1 Simona Halep lost in straight sets.
Wozniacki defeated Swedish qualifier Rebecca Peterson 6-4, 6-1, making just nine unforced errors to Peterson's 36.
In the evening session, 2016 runner-up Dominika Cibulkova of Slovakia ousted Halep 6-0, 7-5, and Czech qualifier Katerina Siniakova upset defending champion Caroline Garcia 3-6, 7-6 (5), 7-6 (4).
Halep said before the tournament that she was struggling with a back problem.
Wozniacki made early exits in her last five tournaments, including three first-round losses. She last reached the third round at the pre-Wimbledon warmup in Eastbourne, where she won.
She next faces Olympic gold medalist Monica Puig from Puerto Rico, who beat Aliaksandra Sasnovich 6-2, 6-2.
Wimbledon champion Angelique Kerber beat Madison Keys 6-0, 4-1 after the American retired due to a left knee injury. In the round of 16, Kerber lined up Ashleigh Barty, last year's finalist.
Two-time Wuhan Open winner Petra Kvitova cruised past Aleksandra Krunic of Serbia 6-3, 6-4.
For Kvitova, the win avenged a stunning upset to Krunic in the third round of the 2014 US Open, their only previous meeting.