The 36-year-old, who says her black bodysuit makes her feel like a super hero, had to call on some of her vintage super powers to get past Ashleigh Barty.
Australian Barty, the 17th seed, broke the 23-time grand slam winner in the sixth game and, when she served out the set convincingly things looked ominous for Williams.
After all, the former world number one had not played a major tournament since winning the 2017 Australian Open, having given birth to her daughter in September.
But from somewhere Williams got her serve firing and summoned up her powerful groundstrokes to blow Barty away 3-6 6-3 6-4.
“I lost the first set and I thought ‘I’ve got to try harder’,” she said. “Then Serena came out.
“Every day is a great day for me and I’m excited to play singles, or doubles, and fight my heart out.”
Williams will face 11th seed Julia Gorges of Germany in round three.
If Maria Sharapova is to win a third Paris title she seems intent on doing it the hard way.
The Russian lost six games in a row during her first-round victory over Richel Hogenkamp and had to dig deep again to beat Donna Vekic in round two.
Serving for the first set at 5-3, Sharapova allowed the world number 52 from Croatia to break back before eventually getting over the line 7-5.
She dropped serve early in the second, and later served for the match at 5-3 again, with the same outcome.
However, Sharapova recovered to triumph 7-5 6-4 to keep her first Roland Garros campaign in three years on track.
This time last year Sharapova had recently returned from a 15-month doping ban, but she had not built her ranking high enough to qualify and was not offered a wild card.
But 12 months later Sharapova is back in the world’s top 30, seeded 28th at Roland Garros and a potential challenger for the title. “Overall, in the moments when I needed to come through, I did.”
In the men’s tournament, Rafael Nadal dropped just four games in a comprehensive 6-2 6-1 6-1 victory.
Nadal will face France’s 29th seed Richard Gasquet in the third round.
Marin Cilic saw off Hubert Hurkacz of Poland 6-2 6-2 6-7 (3/7) 7-5.
Juan Martin del Potro was also a winner in straight sets, the Argentinian fifth seed beating France’s Julien Benneteau 6-4 6-3 6-2.