French Open champion Garbine Muguruza survived a fierce challenge from US teenager Kayla Day Sunday to reach the fourth round of the WTA Indian Wells hard court tournament.
The seventh-seeded Spaniard had to dig in to subdue the hard-hitting Californian 3-6, 7-5, 6-2 and set up a meeting with 10th seeded Ukrainian Elina Svitolina.
Day, last year's US Open junior champion, had reached the third round with an upset of Australian Open semi-finalist Mirjana Lucic-Baroni.
She needed little more than half an hour to seize a set from Muguruza, whose progress so far in 2017 has been hindered by injuries.
Muguruza saved break points in the fifth and 11th games of the second set, finally converting her own first break chance to force the third.
By then Day was wilting in the baking heat of Stadium Court. Muguruza broke her in the second game of the final set and again in the final game as the left-handed youngster surrendered with a double-fault.
"I think she played very good," Muguruza said. "She served very well. I think the first set I didn't play good. My level was not there. My shots were not there, and right away she took advantage and she won.
"I didn't let that frustrate me. I reset my mind. I think at the time I was playing a little bit better and better, even though that first set was a little bit bad. But I think she played good.
"I'm surprised with how she handled center court," added Muguruza, who was astonished -- and touched -- to learn that Day had named one of her dogs Garbine after seeing the Spaniard play at the Australian Open several years ago.
If that youthful admiration made it harder for Day on the court, Muguruza said, it was a problem many on the WTA face.
"I feel the same," she said. "When I play with all those big names and they are older than me. That's being very lucky to play with your idols."
Muguruza will face a dangerous challenge from Svitolina, a two-time winner on the WTA tour this year who took her winning streak to 15 matches with a 6-2, 6-1 win over Australian Daria Gavrilova.
"I'm trying not to think about whether this is my best tennis," Svitolina said. "I've achieved a lot of what I wanted, so I'm happy that I'm keeping it going."
In other women's matches Sunday, third-seeded Karolina Pliskova, inserted at the top of the draw after Serena Williams's late injury withdrawal, edged Romanian Irina Camelia Begu 6-4, 7-6 (7/2).
Pliskova next faces Switzerland's Timea Bacsinszky, who beat Kiki Bertens of the Netherlands 6-3, 5-7, 7-6 (10/8) that produced multiple match points for both players.
Bacsinszky had her first chance to close it out with two match points in the second set.
Bertens had three match points as she served for the contest in the ninth game of the third -- and she had a fourth match point in the tiebreaker before Bacsinszky finally sealed it on her sixth match point.
France's Caroline Garcia rallied from a set down to defeat 11th-seeded Briton Johanna Konta 3-6, 6-3, 7-6 (7/1) and book a meeting with eighth-seeded Russian Svetlana Kuznetsova.
Kuznetsova downed Italian Roberta Vinci 6-2, 2-6, 6-1.