INDIAN WELLS — World No. 2 Simona Halep survived a tough challenge from Ukrainian qualifier Kateryna Kozlova to win third round match 7-6(3), 7-5 at the BNP Paribas Open Sunday.

The Romanian finally put away the 114th ranked Kozlova with eight consecutive points in the second set, a backhand winner proving the decider just as it had in the first set.

The tournament lost 23-times Grand Slam winner Serena Williams, who retired against Garbine Muguruza with what organizers described as a viral illness. The Spaniard was ahead 6-3, 1-0 at the time.

“Before the match, I did not feel great, and then it just got worse with every second; extreme dizziness and extreme fatigue,” Williams said in comments released via tournament organizers.

Halep said her opponent had been tough to put away.

The victory advanced the French Open champion, who won Indian Wells in 2015, to the fourth round for the fifth time in six years.

Former Wimbledon and French Open champion Muguruza was happy with the way she had been playing against Williams before the American’s retirement.

“I think I played well,” she said. “I’m going to take the positive side of that.”

Sixth seed Elina Svitolina, looking for her first title of the year, beat Daria Gavrilova 7-5, 6-4 to advance while world number seven Kiki Bertens reached the fourth round at Indian Wells for the first time after a 7-6(10), 6-4 win over Briton Johanna Konta.

Bertens will next meet Spain’s Muguruza.

“Konta today, she can play really aggressive, and I think with Muguruza it’s the same,” she said. “So I have to serve well, go for my shots myself again where I can, and hopefully play a little better than today.”

China’s Qiang Wang and Australia’s Ashleigh Barty also advanced. — Reuters