Williams will open a doubles match against sister Venus on Wednesday.
Williams will face world No. 2 Anett Kontaveit of Estonia in the singles round of 64, also on Wednesday. This will be the first meeting of their careers.
After early wits with her serve on Monday night, Williams won 10 of the last 13 against Kovinić, the 27-year-old from Montenegro, who is ranked 80 in the world.
After the match, during a ceremony to celebrate her tennis career, Williams said she got a boost from a crowd of nearly 24,000. “The crowd was crazy,” she said.
Williams double fouled twice in the first set but eventually increased his first serve rate to 66%. She won 33 of the first 43 serve points.
A pivotal moment came in the sixth game of the first set when Kovinić appeared on the verge of a 4-2 lead. But a Williams shot that looked long and wide was not, hitting the back of the end line and the outer edge of the singles touchline. This was the first of Williams’ 11 points in line as she made it through the rest of the way.
It was Williams’ third match since announcing she would “grow away from tennis.”
“I’ve never liked the word retirement. To me, it doesn’t sound like a modern word. I thought this was a transition, but I want to be sharp about how I use the word, to mean a transition. something very specific and important to a community of people,” Williams said in a Vogue article published earlier this month.
“Perhaps the best word to describe what I’m doing is evolution. I’m here to tell you that I’m evolving from tennis, towards other things that are important to me,” she said.
Williams, 40, said Monday night it was a difficult decision.
“I think when you’re passionate about something and you love something so much, it’s hard to let go,” she says. “Sometimes I think it’s harder to walk away than not. That’s the case with me.”
When asked by Gayle King what victory would bring her in the future, Williams pointed to her venture capital firm and also said she wanted to work on her spiritual life.
Williams’ singles win was witnessed by her husband, Alexis Ohanian, and their daughter, Olympia, with the youngster wearing a white necklace in her hair, reminiscent of Williams’ look when she won the title. first of six US Open titles as a teenager in 1999.
“I look forward to waking up and just saying, OK, I don’t need to run to court today,” Williams said. “I want to be a mother. She’s such a good girl. I just want to be a good mother to her.”
CNN’s Jill Martin contributed to this report.