"So that is the biggest difference".
Anyone who's paying attention would echo that sentiment. Thursday, she tapped into muscle memory and edged closer to that most familiar and formidable opponent.
Barty needed just 64 minutes to live up to her first-time seeding at Roland Garros, while also showing no signs of the back problem that had her in doubt for the clay-court major.
"I just said I got to be better, I got to fight harder", she told Tennis Channel after the match.
When last seen in an official event, Williams was striding off the court in Key Biscayne and directly into a waiting vehicle after a disappointing Miami Open loss to Naomi Osaka.
She instantly broke back after anticipating a Barty attack with the Aussie stranded out wide, graciously lapping up the gift of an empty court to roll the ball into.
The last time Serena Williams played a Grand Slam match, Andy Murray was the fellow singles world No 1, Maria Sharapova was serving a ban, Roger Federer had not won a Major in around five years and Jelena Ostapenko was a Latvian teenager who hadn't lifted a single tennis trophy as yet.
"I couldn't play previous year".
The very first game featured an ace at 112 miles per hour (181 kph) and when it ended with Pliskova netting a backhand, the chair umpire intoned, "Jeu, Madame Williams", French for "Game, Mrs Williams", a change from the "Mademoiselle" officials use for unmarried female players. Her daughter was delivered via emergency C-section due to fetal distress, and the surgery gave Williams complications that were so severe she nearly died.
She called herself "the world's worst practicer".
Serena Williams is back, ladies and gentlemen.
"I don't know how many aces there were", Williams smiled courtside after the match. It's not even remotely true.
I'm concerned about Serena's conditioning, as it catches up to everyone who isn't consistently playing.
"Catsuit anyone? For all the moms out there who had a tough recovery from pregnancy-here you go", Williams tweeted alongside a photo of herself on the court.
Barty was a doubles finalist in Paris a year ago but has never advanced past the second round in singles here. The men's tournament sees rising Canadian star Denis Shapovalov play his first French Open main draw match against Australian John Millman, while third seed Marin Cilic faces world number 1,072 James Duckworth.
When Williams served out the victory with a backhand victor down the line, she raised both arms overhead and held up her left fist as she approached the net to meet Barty.
The fashion statement, this time in the form of a black bodysuit with a red waistband. But as any working mother can attest, readiness can be a shifting target and everyone has to wing it to a certain extent.