Maybe she is saving the growl for the final against tenacious Romanian former world number one Simona Halep when, for the third time, she will stand one win away from matching Margaret Court's 24 Grand Slams singles titles. She also needs to stay positive and remind herself that A. She has won a major more recently than Serena B. Serena has not met the moment in her last two major finals and C. she is the superior mover.
It was a far cry from the stuttering performance Williams showed in her three-set quarter-final against compatriot Alison Riske on Tuesday, who was able to drag Serena into the type of dogfight Strycova - Johanna Konta's conqueror in the quarters - was unable to muster.
The size of the challenge confronting her is reflected in having won just one of her 10 previous meetings with Williams, although she has regularly taken her to three sets.
"I was calm today", she said, then rolled her eyes and added: "It's a day-to-day basis with me".
"Of course, I don't have as much power as Serena, but I have other weapons", said Strycova.
She finally silenced the 'she's number one, when will she win a Grand Slam?' questions a year ago when she won her maiden major at the French Open, which came after three final defeats and with a reputation as a choker.
In the Open Era, only 10 other players have pulled this feat off, with Chris Evert having done it the mosttimes with six and Williams now tied on four with Stefanie Graf.
It's been an up-and-down year because of illness and injury, limiting Williams to 12 matches until last week. "Now that I am past older, I feel a little bit less pressure".
"I thought about it this morning", she said.
Williams played cleanly, accumulating almost twice as many winners as unforced errors, 28-10. At Flushing Meadows, she was outplayed by Naomi Osaka in a match that descended into chaos after Williams was docked a game for a heated argument with the chair umpire.
"We all know that". We will see what is going to happen.
While Williams is chasing a place in the history books, Halep has her own points to prove.
Breaks in the fifth and seventh games of the second set confirmed the gulf between this unlikely semifinal pairing, with Williams sealing victory when Strycova could only poke a serve back over the net and watch it returned with interest into an empty court.
Five of the first 11 points lasted at least 10 strokes; two went 23. Or that Williams soundly beat Halep later at that same tournament.