PARIS — Serena Williams has advanced to the fourth round at the French Open with a seesaw win over 18-year-old Russian Anastasia Pavlyuchenkova 6-1, 1-6, 6-2.

The top-ranked Williams appeared in danger when she lost the first five games of the second set Saturday. At that point, she received a visit during the changeover from a trainer, who checked her temperature and gave her pills.

Williams' play steadied in the third set. She took a 4-1 lead, and on match point put a booming return at Pavlyuchenkova's feet for the win.

It assured Williams of retaining the No. 1 ranking after the tournament.

The 18-year-old Pavlyuchenkova fell to 8-1 this year in three-set matches.