Williams beat Zarina Diyas of Kazakhstan 7-5 6-3 in her first-round match at Indian Wells.
The 23-time Grand Slam singles champion said: “It definitely wasn’t easy but it was good. I’m a little rusty but it doesn’t matter. I’m just out here on this journey doing the best I can.”
In her straight-sets win, Williams hit 27 unforced errors and 34 winners in front of a large crowd in California.
Williams played aggressively and broke Diyas five times in the match that lasted 92 minutes.
Her previous appearance was in 2017 when she won the Australian Open while pregnant.
Speaking about her comeback, she said: “It was incredible. It’s been over a year and a kid later. I get to go home to her now and I’m excited about that.”
The 36-year-old gave birth to daughter Alexis Olympia in September last year, but says she almost died after post-childbirth health complications that included blood clots in her lungs.
“It is a journey for me and I am just going to go for it,” she said. “I wanted to stay fit and just be ready.
“I wasn’t ready to retire yet even though it would have been a great way to retire.”
Williams is unseeded at Indian Wells, meaning she had to play in the opening round while the seeded players enjoyed a bye.
Serena plays 29th seed Kiki Bertens in the second round, knowing that she could face sister Venus in the third round if both progress.