The exhibition contest in Abu Dhabi against Jelena Ostapenko was the American’s first match for 11 months.
Williams struggled with her movement at first but played some fine shots in a 6-2 3-6 (10-5) defeat.
Asked about the likelihood of defending her title at the Australian Open, which starts on 15 January, Williams said she was “taking it one day at a time”.
Ranked 22nd in the world, she would not need a wildcard to play in the first Grand Slam tournament of the new season.
“I’m going to assess everything with (coach) Patrick (Mouratoglou) and my team and go from there,” she added.
“I don’t know if I’m totally ready yet or not. When I come back, I definitely want to be competing for championships.
Williams, who gave birth to her daughter in September, had not played since winning her 23rd major singles title in Melbourne last year.
“I think everything is so much easier for me having my daughter at home waiting for me and knowing that I’ve won 23 Grand Slam singles titles,” said Williams.
“I don’t have anything to prove but I just want to go out there and play. I’m not done yet.”
Williams initially struggled to get enough power behind her serve and missed several straightforward shots as French Open champion Ostapenko claimed the first set.
The Latvian pushed her opponent wide, with Williams’ movement looking sluggish at first.
However, she found more timing as the match progressed, increasing the speed on her serve and moving well inside the court.
A fine lob over Ostapenko was the highlight of the second set but the Latvian, who stunned Simona Halep at Roland Garros in June, overpowered her in the tie-break. (Courtesy BBC)