"I was really happy with how I just fought for every point no matter how I was playing," said Williams, joking that it felt like she hadn't won a match in straight sets "since the '90s".
It has been more than three years since Williams won her 23rd grand slam title at the 2017 Australian Open — when she was already pregnant with daughter Olympia.
She has come close since, reaching four major finals only to come away empty-handed.
Williams needs one more to equal Margaret Court's record and her chances should be improved by the absence of several top players because of coronavirus concerns or injury.
World No 1 Ash Barty, the second-ranked Simona Halep and Canadian Bianca Andreescu — who stunned Williams in last year's final — are all absent from the behind-closed-doors tournament.
A title win for Williams would also see her become the most decorated women's player at the US Open in the modern era.
She is currently tied with Evert for most US Open women's titles with six.
