Serena Williams began her pursuit of a record-equalling 24th Grand Slam singles title with a dominant 7-5 6-3 win over fellow American Kristie Ahn.

Williams gathered momentum late on, winning four straight games against the world number 96 in the second set.

"I was really happy with how I fought for every point," she said.

"No matter how I was playing, I just had to get my Serena focus back so that was what I was working on today."

Men's second seed Dominic Thiem also advanced, having been leading 7-6 (8-6) 6-3 when Spanish opponent Jaume Munar retired from the match.

Thiem, 26, will face Indian world number 124 Sumit Nagal in the second round as he looks to capitalise on the absence of Roger Federer and Rafael Nadal to win a maiden Grand Slam title.

Women's 10th seed Garbine Muguruza sealed her place in the second round with a 6-4 6-4 win against Japan's Nao Hibino.

Seventh seed Madison Keys is through after beating Hungary's Timea Babos 6-1 6-1, while American second seed Sofia Kenin claimed a 6-2 6-2 victory against Belgium's Yanina Wickmayer.

'I love my job' - Williams

With six of the world's top 10 absent from the women's draw because of the coronavirus pandemic, Williams has a prime opportunity to claim the 24th title she has been chasing since her last win at the 2017 Australian Open.

The third seed will face world number 117 Margarita Gasparyan of Russia in the second round, with the trickier challenge of compatriot Sloane Stephens possibly awaiting her after that.

Williams had to overcome some inconsistencies, gifting Ahn two breaks of serve, but brushed aside the suggestion that the lack of fans on Arthur Ashe Stadium had affected her level of play.

"It's quiet," she said. "It's such a good stadium. It's a Grand Slam and I think I'm still as passionate and intense out there.

"I love my job. I love what I do. You can't do it forever even though I've kind of been doing it just over forever. One of these days it's going to end and I love being out here."