Caroline Wozniacki said she was "definitely a little rusty" following her first-round victory at the Canadian Open on her return to tennis after retiring in 2020.
The former world number one, 33, has since given birth to two children and beat qualifier Kimberly Birrell of Australia 6-2 6-2 in Montreal.
"It feels great," said Wozniacki.
She will face either Wimbledon champion Marketa Vondrousova or Egypt's Mayar Sherif in the second round.
"What an amazing place to come back and play my first match," added Wozniacki. "I love playing here in Montreal."
In June, the Dane announced her desire to play in this year's US Open. She reached the final of the tournament in New York in 2009 and 2014.
Soon after the interview with Vogue,external-link Wozniacki was handed a wildcard for the event at Flushing Meadows, which begins on 28 August.
She had not played a competitive match since the Australian Open more than three years ago, and became a mother to daughter Olivia in June 2021 and son James in October 2022.
Wozniacki called her first win as a mum "pretty crazy" and said her children would be "napping right now, which is awesome".
"I'm going to catch them after I do a little bit of treatment and food and stuff," she added. "That's the good part of playing early. I still have the afternoon with them."
Wozniacki dropped the opening game but rallied to take the final four games of the opening set, before securing the match in the second set by breaking 115th-ranked Birrell with a backhand winner.