Then, a few hours later on Centre Court, she went out and played as if she were.
Only a teenager with 23 grand slam title wins already under her belt, one short of Margaret Court’s all-time record.
It was unstoppable. Barbora Strycova did not stand a chance. 6-1, 6-2 and it did not even take Williams an hour.
She was still bouncing with energy in her press conference afterwards – a very different person to the slightly sulky, reluctant subject the media are often forced to suffer.
Williams joked that after every volley she made, she thanked Andy Murray for getting her to play mixed doubles and sharpening her reflexes.
Her sortie into an unfamiliar event has had a more fundamental effect than that, though.
Spending most of the fortnight as merely first lady to the great home hope’s Wimbledon return, Williams suddenly arrived at the second Thursday completely fresh, as though the serious stuff was only just beginning.
Time, finally, to get her business head on.
“The process of sitting down to think this morning was definitely deliberate,” she said. “I was actually thinking about when I won my first Wimbledon. It was against Venus.
“I was trying to tap into those emotions. Trying to tap into that younger Serena, trying to tap into how to win, basically. I was really calm. I remember I hit an ace.
“I thought about how it’s so, so different when you’re younger as opposed to now. Now I just need to relax and do what I can do.
“I was calm today. I’m not always. It’s a day-to-day basis with me. We all know that. I’m far from perfect.
“Even this morning, as I was thinking, other thoughts were popping in my brain. I thought about being my 24th slam.
“But I actually haven’t thought about it since, because it’s really not about 24 or 23 or 25.
“It’s really just about going out there and giving my best effort no matter what.
“I will always have a great career. So I just kind of let it go this morning and I feel really calm about it.”
The new serene Williams is an even more daunting prospect than the usual Serena.
This is her third final since becoming a mum to Olympia just under two years ago and after last year’s defeat to Angelique Kerber was dedicated to mothers everywhere.
“To all the moms out there,” she had said on Centre Court. “I was playing out there for you today and I tried.”
However, having battled thought a long-term knee injury, this year the younger Williams sister is doing it for herself. Simona Halep be warned.
“I’m just playing for me,” she said. “Last year was a really special moment. Olympia was 10 months. So for that it was definitely a different moment.
“This year it’s a different experience and I’m happy to be back. I definitely wouldn’t have predicted it a month ago, but here I am. So perhaps I’m playing for everyone that didn’t predict it a month ago!”