Fourth seed Naomi Osaka overcame a scare to beat fellow Japanese player Misaki Doi in three sets and avoid a major shock in the US Open first round.
Osaka, who won the first of her two Grand Slams at Flushing Meadows in 2018, wobbled in the second set before recovering for a 6-2 5-7 6-2 victory.
Elsewhere, teenager Coco Gauff’s hopes of another Grand Slam run were ended by 31st seed Anastasija Sevastova.
But top seed Karolina Pliskova and sixth seed Petra Kvitova advanced.
Osaka, 22, withdrew from the Western & Southern Open final on Saturday with a left hamstring injury, saying afterwards she was “stressing” about her fitness going into the Grand Slam.
During Monday’s less-than-convincing win over 81st-ranked Doi, she did not wear any strapping or need medical treatment.
“It was difficult [physically]. I knew there was a chance it would get really long. I will have to see what happens tomorrow and how I feel,” Osaka said.
The former world number one struggled with her first serve in the early part of the match, landing only 38% as Doi took control in the second set and threatened to level the match.
But Osaka switched gears with a decider looming, finding more power and precision with her serves and returns to fight back from 5-2 down to level at 5-5.
Osaka was unable to take any of her three break points for a 6-5 lead before the momentum swung back to Doi, who broke on her second set point through Osaka’s 20th unforced error.
However, Osaka increased her level again at decisive moments. She broke in the opening game of the decider, and again for a 5-2 lead, to come through in two hours and three minutes.
Gauff undone by US Open specialist Sevastova
World number 51 Gauff reached the third round at her home Grand Slam in 2019, soon after making Wimbledon’s last 16.
But the 16-year-old American, who had backed up last year’s promise by reaching the fourth round at January’s Australian Open, could not reproduce that form against a relentless Sevastova, 30.
A second-set resurgence looked to put Gauff on track for victory against the Latvian but she lost 6-3 5-7 6-4.
The Latvian – a semi-finalist in 2018 and two-time quarter-finalist – overcame her frustration at narrowly losing the second set after the pair continually exchanged breaks. She surged ahead at 5-4 up in the third to break Gauff’s serve and claim victory.
Gauff was let down by a huge 13 double faults and went out when she netted a return to make her first opening-round exit from a Grand Slam tournament.