French Open champion Ash Barty survived a first-round scare at the US Open on Monday, staving off 25-year-old Zarina Diyas 1-6, 6-3, 6-2 after struggling to find her footing as the action kicked off at Arthur Ashe Stadium.
The unseeded Diyas, from Kazakhstan, took five straight games in the first set, as the world No.2 committed a string of unforced errors and got in just 25 per cent of her first serves.
Barty was able to stop the pain midway through the second set, converting on a crucial break-point opportunity to take a 5-3 lead and reverse the momentum in what had been a one-sided match.
The 23-year-old Australian, who reached the fourth round here last year, appeared to be back on form by the third set, getting in nearly two-thirds of her first serves and firing off 12 winners.
Barty skyrocketed to fame in June at Roland Garros, where she became the first Australian woman in 46 years to win a Grand Slam after downing Czech teenager Marketa Vondrousova in straight sets.
She followed up that performance with a win at the Birmingham Classic and a brief stint atop the WTA singles rankings, before bowing out of the Eastbourne grass court tournament with an arm injury.
Kei Nishikori became the first man to advance to the US Open second round as the 2014 finalist beat qualifier Marco Trungelliti who was forced to retire with the Japanese leading 6-1, 4-1 on Monday.
Nishikori's serve clicked from the start and the seventh seed won 90 per cent of his first-serve points while never facing a break point against the Argentine in 47 minutes on Grandstand.
Next up for Nishikori is a second-round clash with Thiago Monteiro or Bradley Klahn.
Sevastova condemns Bouchard to 12th successive defeat
Latvian 12th seed Anastasija Sevastova dispatched an error-prone Genie Bouchard 6-3, 6-3 to reach the second round.
Bouchard struggled with her accuracy, committing 27 unforced errors and double faulting four times, in the match which drew a big crowd to Court 5.
Sevastova, a semi-finalist in New York last year, was sharper throughout and blazed a crosscourt forehand winner past Bouchard's outstretched racket on match point.
Former world number five Bouchard, who reached the Wimbledon final in 2014, has struggled all season is now ranked a lowly 119 and her loss on Monday was her 12th in a row.