Last year's Wimbledon champion was among several players to retire from the tune-up event in Cincinnati, days after her Montreal quarter-final finished around 3am local time.

"I wasn't feeling the greatest physically after Montreal and Cincinnati, but we had time to recover and then practise again so now I'm feeling well," said Rybakina.

The Kazakh fourth seed powered into the second round in New York with a 6-2, 6-1 win over Ukraine's Marta Kostyuk, partly inspired by the experience of seeing Lionel Messi in the flesh.

Rybakina watched Messi make his Major League Soccer debut on Saturday, the Argentine scoring in a 2-0 win for Inter Miami at New York Red Bulls.

"It was an amazing experience, first time watching soccer live and especially to come and see the legend like Messi, I was happy to be there," said Rybakina.

Beaten in round one a year ago, Rybakina goes on to play either Hungary's Panna Udvardy or Ajla Tomljanovic of Australia for a spot in the last 32.

"I'm feeling much better and we're going to take it a day at a time. Hopefully I continue like this physically," said Rybakina, who has yet to go beyond the third round at the US Open.