Karolina Pliskova roared back from a set down to outlast Olympic gold medallist Monica Puig 1-6 6-4 6-4 as the Czech third seed avoided a major upset at the BNP Paribas Open in California on Friday.
Pliskova, after falling behind 3-0 in the third set, fought through a long sixth game to help turn the tide and won six of the last seven games to advance to the third round.
"I'm definitely happy I had my serve today; it was working with me, especially in the third set when I was 0-3 down," she said in a courtside interview.
"She was playing really well, hitting the balls really fast and deep, making it tough for me to play my game."
Puig, from Puerto Rico, had never taken a set from Pliskova, but broke her Czech rival four times to sweep the opening set.
Pliskova used several service breaks of her own and served out the second set to level the match.
The Czech had 19 winners to 34 unforced errors and converted five of her seven break point opportunities in the match.
Puig's 37 unforced errors cancelled out her 32 winners.
French Open champion Garbine Muguruza, the seventh seed, had slightly easier time as the Spaniard survived some nervous moments before defeating Belgian Kirsten Flipkens 6-2 6-3 in her opening round match.
The win set up a meeting with U.S. teenager Kayla Day, who surprised Australian Open semi-finalist Mirjana Lucic-Baroni of Croatia in three sets 6-4 5-7 7-5.
After taking the first set and grabbing a 5-0 lead in the second before Flipkens rallied, Muguruza broke through for the sixth and final time in the match, striking 24 winners to 28 unforced errors.
"It was a difficult match," Muguruza said post-match. "She's very talented and she can hit some critical shots and she can be tricky."
The Spaniard won her third straight match against her rival on a hard surface after splitting their first four meetings, losing twice on grass.
"It's always difficult to close out your first match," Muguruza said. "She's a very talented player, unbelievable, with a very different game. I got nervous!"
Day, 17, won the final four games of her match with the 32nd-seeded Lucic-Baroni to claim victory.
"I started to really believe I could win at 6-5 in the third," said Day. "It was still a really tough game, because I was a little bit tight to close it out. But my serve had been giving her a lot of problems, so I knew if I stuck to my game it might work out."
Among other top-seeded players, Dominika Cibulkova of Slovakia and Ukrainian Elina Svitolina had the toughest assignments.
Fifth seeded Cibulkova outlasted Latvian Jelena Ostapenko 6-4 3-6 6-3 and the 10th seeded Svitolina needed three sets to defeat Wang Qiang of China 3-6 6-3 7-6(3).
Russian Svetlana Kuznetsova, the eighth seed, defeated Johanna Larsson of Sweden 7-6(3) 6-4, and 11th seeded Johanna Konta prevailed 6-4 6-4 over Heather Watson in a meeting of British players.
(Reporting by Gene Cherry in Salvo, North Carolina; editing by Amlan Chakraborty)