Serena Williams drew on her "superhero" powers to produce a stirring fightback and beat Ashleigh Barty in the second round of the French Open.

The 23-time grand slam singles champion said a new Wakanda-inspired catsuit she is sporting at Roland Garros made her feel like a "warrior princess" after beating Kristyna Pliskova in the first round.

Barty gave an out-of-sorts Williams a reality check as she won the first set, but the 36-year-old showed quality and spirit that has made her one of the greats by roaring back to win 3-6 6-3 6-4.  

Williams, unseeded in her first grand slam less than nine months after giving birth to her first child, showed no signs of fatigue on Court Philippe Chatrier, sealing victory under fading light after 9pm in Paris.

Julia Goerges will be the next opponent for an inspired Williams, who also won her only previous meeting with 17th seed Barty at the Australian Open in 2014.

Barty said she viewed facing the imperious Williams as an opportunity and the Australian appeared determined to grasp it, making a confident start.

Williams looked a little flat and drilled a wild forehand long to go 4-2 down, the composed Barty breaking to love to take the upper hand.

Barty did not give her esteemed opponent a look-in, Williams failing to find her range and going a set down when she failed to return a powerful serve.

Another unforced error gave Barty a break in the first game of the second set and there were gasps from the crowd when Williams hammered an overhead way beyond the baseline.

Williams fired herself up to turn the tide, though, showing great defence and anticipation to put away a forehand for an immediate break back before letting out a roar after a rasping backhand winner put her a break up at 3-1.

The three-time French Open champion was moving much more freely, bossing the majority of rallies from the baseline and clenched her fist after a venomous ace took it to a decider.

Williams maintained the momentum, a Barty backhand into the net put her a break up at 2-1, and showed no further signs of a lack of match practice.

Barty was peppered by brutal groundstrokes and could not find a way back, Williams letting out another scream of delight after holding to love to go through.