INDIAN WELLS, United States (AFP) - World number two Simona Halep survived a strong challenge from Ukrainian qualifier Kateryna Kozlova Sunday (March 10) to reach the WTA fourth round at Indian Wells Romania's Halep, who won the title in the California desert in 2015, struggled to hit her stride but emerged with a 7-6 (7/3), 7-5 victory in her first meeting with the 114th-ranked Kozlova.
"It was really difficult against her because I never played against her - it was a bit difficult to get a rhythm," Halep said.
"I'm really pleased I could win in two sets."
Service breaks were the order of the day as Halep and Kozlova traded four on the way to the first-set tiebreaker and four more to open the second set.
Halep's two holds - sandwiched around another break of Kozlova's serve - put the Romanian up 5-2 but she was broken serving for the match and needed one last break of Kozlova's serve in the final game to clinch it with a backhand up the line.
Halep next faces either 22nd-seeded Latvian Jelena Ostapenko or Czech Marketa Vondrousova, the world number 61 who ousted 2018 Indian Wells finalist Daria Kasatkina in the second round.
US 10th seed Serena Williams was also fighting for a fourth-round berth on Sunday.
The 23-time Grand Slam champion, who defeated Victoria Azarenka in a battle of former world number ones in the second round, had another ex-No. 1 waiting in Spain's Garbine Muguruza.
"I always have the toughest draw," Williams said ruefully. She has won three of her five matches with the Spaniard, including the 2015 Wimbledon final, but fell to Muguruza in the 2016 French Open final in their most recent meeting.