Serena 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 to Muguruza.
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."
Muguruza, currently ranked 20th in the world, was sorry to see the match end the way it did, even though it put her through to a fourth-round meeting with seventh-seeded Kiki Bertens of the Netherlands, a 7-6 (12/10), 6-4 winner over Britain's Johanna Konta.
"We've played many times and it's always super-tough, super-exciting," Muguruza said of Williams. "I wish I'm going to see her soon and feeling better."
In fact their five prior meetings all came in Grand Slams, the last two in finals. Williams beat the Spaniard for the Wimbledon title in 2015 and Muguruza walked off with the 2016 French Open crown.
It was a tough draw for Williams, who defeated former world number one Victoria Azarenka in her second-round opener.
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.
"It was really difficult against her because I never played against her - it was a bit difficult to get a rhythm," Halep said.
There were service breaks aplenty 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.
"When I was leading the match, she played without fear, I felt like she was playing much better in those games," Halep said.
"It was difficult for me to close those sets, but I'm actually proud that I could do that," added the Romanian.
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.