nSerena Williams's first tournament since the Australian Open came to an abrupt end on Sunday as the ailing 23-time Grand Slam champion retired from her third-round WTA match against Garbine Muguruza at Indian Wells.

Muguruza was leading 6-3, 1-0 when Williams called it a day in the battle of former world number ones because of a viral illness.

"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.

The 10th-seeded American, continuing to work her way back up the rankings in the wake of time off to have a baby, had made a strong start, winning the first three games.

But she called for the trainer after dropping six straight.

After a long talk with medical personnel Williams took the court for the second set, but after Muguruza held serve at love Williams called a halt.

"By the score, it might have looked like I started well, but I was not feeling at all well physically," Williams said. "I will focus on getting better and start preparing for Miami."

It was the sixth meeting between Muguruza and Williams, all five prior coming in Grand Slams.

The Spaniard, who advanced to a fourth-round clash with seventh-seeded Kiki Bertens of the Netherlands, a 7-6 (12/10), 6-4 winner over Britain's Johanna Konta.

World number two Simona Halep had her hands full with Ukrainian qualifier Kateryna Kozlova but emerged with a 7-6 (7/3), 7-5 victory in her first meeting with the 114th-ranked player.

Halep next faces 61st-ranked Czech Marketa Vondrousova, who followed up her win over 2018 finalist Daria Kasatkina with a 4-6, 6-3, 6-4 win over 22nd seed Jelena Ostapenko of Latvia.

Sixth-seeded Elina Svitolina also advanced, holding of Australian Daria Gavrilova 7-5, 6-4.