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.
