Russia's Elena Vesnina, last week's winner at Indian Wells, crashed out of the WTA Miami Open in the second round on Friday at the hands of Croatian qualifier Ajla Tomljanovic.
Vesnina, seeded 13th, faced rain delays and wind during her closely fought contest but ended up losing 3-6, 6-4, 7-5 to 594th-ranked Tomljanovic, who will face Czech Lucie Safarova in the third round.
American qualifier Taylor Townsend upset Italian 25th seed Roberta Vinci 6-3, 6-2.
The 20-year-old left-hander's victory over the 2015 US Open runner-up was among her top career triumphs and sets up a possible meeting with seventh seed Svetlana Kuznetsova of Russia.
Indian Wells finalist Kuznetsova must get past Luxembourg's Mandy Minella in her second-round contest to reach the third-round meeting with world number 111 Townsend.
"I played really well and I am happy with that result," Townsend said of her victory over Vinci. "I've had some tough matches here. I think I was a lot more solid than I have been in the last couple of days.
"All the things that didn't really work... it came together today."
Townsend has never played Kuznetsova, the 2004 US Open and 2009 French Open champion, and acknowledged it would be a huge challenge.
"I really like watching her play," Townsend said. "She has won two Slams and is a great player who is playing some of her best tennis now. I am playing well. I've got four matches under my belt and I don't have anything to lose."