Reigning French Open champion Ashleigh Barty shook off a horrid first set to defeat Kazakhstan's Zarina Diyas 1-6, 6-3, 6-2 on Monday in the first round of the US Open.
The Australian second seed advanced to a second-round match against America's 73rd-ranked Lauren Davis or 171st-ranked Swedish qualifier Johanna Larsson.
Czech third seed Karolina Pliskova also struggled into the second round, while 2014 runner-up Kei Nishikori of Japan needed only 47 minutes to advance.
Pliskova held off 138th-ranked Czech qualifier Tereza Martincova 7-6, 7-6 after an hour and 46 minutes.
"It's tough to play Tereza," Pliskova said. "We never played and especially tough to play in the first round. Not my best performance today for sure, and she made some great shots."
Seventh seed Nishikori reached the men's second round 6-1, 4-1, when 205th-ranked Argentine qualifier Marco Trungelliti retired with a back injury.
"It's a little bit sad to see. He's a great player," Nishikori said of his stricken opponent. "For me, I played great tennis from the beginning and I'm happy with the way I played today."
Pliskova and her compatriot exchanged breaks of serve through the first six games of their match, Martincova breaking again for a 5-4 edge and coming within two points of taking the set before Pliskova rallied and broke back to equalize at 5-5.
Pliskova took the first tie-breaker with forehand winners on the final two points, then squandered a 3-0 edge in the second set before taking the final four points of the last tie-break, smashing a service winner to claim the match.
"Not happy that I lost three breaks of serve in a row. That's not possible for next time," Pliskova said. "I'm happy I could get through. And happy to win in two tie-breaks. That hasn't happened for a long time."
Pliskova, Barty, Wimbledon champion Simona Halep and top-ranked defending champion Naomi Osaka all have a chance to stand atop the rankings at the end of the US Open.
Men's former world No 4 Tomas Berdych was a high-profile departure on the first day, the Czech going down 6-1, 2-6, 6-4, 6-4 to American qualifier Jenson Brooksby.
Berdych has been struggling with a back injury for the past 14 months and entered the US Open under a protected ranking. Based on his performance against Brooksby, it is clear the former Wimbledon finalist is still some way short of match fitness.
