The American's 23 majors speak to her immense powers on the tennis court and she engineered an out-of-this world comeback at the French Open against Ashleigh Barty on Thursday to reach the third round.
Barty -- the 17th-seeded Australian with a serve nearly as imposing as Williams' -- looked on course for the biggest victory of her career when she claimed the first set and led by a break in the second.
But Williams -- as she has done so often in her career -- rallied for a 3-6 6-3 6-4 win as light faded in the Parisian evening.
The gripping tussle on Philippe-Chatrier court concluded at around 9:15 p.m. local time.
"I think when push came to shove, the real Serena came out," Barty told reporters. "And that's one of her best assets is, when her back is against the wall, the best comes out."
Where does that come from?
"I have definitely always had that will to win," new mum Williams told reporters. "It was something I was born with, thank goodness.
"This is a grand slam, my first one back. I want to do the best that I can. I want to be able to just do my best and one day tell my daughter that I tried my best. When I was out there, that's all I was trying to do."
Lack of matches
Despite those nearly two-dozen grand slam titles, if Barty had prevailed it could hardly have been classified a massive upset.
None came on clay, either, a specialized surface where moving can be difficult, unlike hard courts.
And Williams -- down to 451st in the rankings due to her tour inactivity -- was facing a different Barty than the one she defeated at the 2014 Australian Open for the loss of only three games.
After taking a break from tennis as it all got too much for the junior Wimbledon winner, Barty enjoyed a breakthrough 2017.
Her first serve fired as the opening frame unfolded while Williams was struggling. Barty's low slice caused havoc, Williams erred on overheads and dumped make-able volleys into the net.
Her first-set tally read three winners and 12 unforced errors.
The first game of the second set brought yet more miscues and Williams was broken to love.
Then came the turnaround.
On break point in the ensuing game, with a short forehand and Williams out of position, Barty directed her shot at her opponent instead of putting it away down the line.
Williams duly sent her own forehand into the open court for 1-1.
Of the 159 points in the match, that could have been the most important.
There was simply no stopping Williams afterward, roars of delight and fist pumps confirming the shift. Barty, meanwhile, was rattled and the 22-year-old never regained her form of the first set.
In the final two sets Williams, whose next foe is 11th seed Julia Goerges, compiled 25 winners and 24 unforced errors.
"I think she's not quite at the level she was when she was at her best, but that's normal," Barty said. "But her level when she's not quite on her best is still bloody good."
Williams acknowledged she is still seeking top form but is adamant she will find it.
"I'm probably not where I was before I left," said Williams. "But the good news is I feel like I'm definitely going to get there. And I don't want to get there, I want to get beyond there. I don't want to limit myself. That's what I want to look forward to doing."
Williams has been closer to defeat at grand slams in the past.
At the Australian Open, for example, in 2007 -- the last time she was unseeded at a major -- Nadia Petrova and Shahar Peer were within a whisker of ousting Williams. Williams didn't buckle and beat Maria Sharapova in the final.
And at the French Open in 2015, when Williams dealt with illness, she overturned set deficits four times. In the final, Lucie Safarova led by a break in the third set prior to Williams' charge.
Serena Williams came back to beat Ash Barty at the French Open on Thursday.
Yet this comeback, with her time away from the game, playing on clay -- just three of her 23 grand slam titles have come at the French Open -- and how the first set unfolded, has to be right up there.
Elsewhere, Sharapova -- a possible opponent of Williams' in the fourth round -- relinquished leads in both sets but still beat Donna Vekic 7-5 6-4 and top-ranked Simona Halep thumped Taylor Townsend 6-3 6-1.
In the men's draw, 10-time champion Rafael Nadal cruised past Guido Pella 6-2 6-1 6-1, with Dominic Thiem -- perhaps the Spaniard's main threat -- completing a four-set win over Stefanos Tsitsipas 6-2 2-6 6-4 6-4.
Rafael Nadal crushed Argentina's Guido Pella at the French Open.
Nadal next encounters friend and French hope Richard Gasquet, against whom he holds a 15-0 record.
Back to Williams and who is to say she can't keep it going at Roland Garros?
She is still, after all, wearing that 'superhero' outfit.