Greinke brought an unexpected element of entertainment after he was heard calling his own pitches and giving hand signals to catcher Martin Maldonado, essentially tipping off the Giants' hitters.
The calls were picked up on the microphones and the announcers even noticed it.
"He told everybody what signs they're going with," said analyst Geoff Blum.
Still, even though he helped out the batters throughout the game as a runner was on second, Greinke managed to strike out seven.
But why would Greinke give up the signs? Some people on Twitter tried to allude to it as penance for the sign-stealing scandal that rocked the Houston team and the league.
Hysterical, Greinke calling his own pitches out-loud, apparently trying to make up for past Astros indiscretions. Greinke is the anti-Astro, they stole signs, he gifts them.— Walt Deptula (@deptulahasrage) August 13, 2020
As much as some would like for that to be the case, Greinke offered a far simpler answer after the game Wednesday night.
"I don't like to take a long time with a man on second base, especially inside. I'm trying to find ways to speed that up, but so far this year has been good but it got messed up today," said Greinke, referencing confusion in the seventh inning.
"It happens to me a decent amount where I shake a lot with a man on second, and then it gets confusing. And then the catcher will call timeout because we've messed up so many times. And then it takes, like, over two minutes, maybe even, like, four or five minutes sometimes just to throw one pitch, and it's not something I like but something that's happened, probably, like, five times now, and I don't like doing it," he continued.
Maldonado didn't seem to have a problem with Greinke calling the signs, either, saying that decision was "pretty smart."
Maldonado helped lift the Astros to their 5-1 victory, hitting a 3-run homer backed by Greinke's strong start.
Astros manager Dusty Baker also weighed in on Greinke's talent.
"You probably won't see another guy like Greinke in your lifetime or my lifetime either. This guy sure can pitch," Baker said.
People on Twitter appeared to echo Baker's feelings, with some calling Greinke "magnificent" and even a "legend."
Zack Greinke was magnificent!! He literally was telling his pitch out and still got the outs. He pitched strong and our bullpen came through!! This game shows us one thing. The only one that can beat us, is us. No team will ever beat us.— 𝗠𝗮𝗿𝗶𝗼 👑🍊⚾️ #ForTheH (@therealmcortez) August 13, 2020
Zack Greinke: Calling out the signs. 😂— Rob Friedman (@PitchingNinja) August 13, 2020
And don't think the Astros shied away from what their starter was doing. They played it up after the game, playing on a Stevie Wonder classic for tweet inspiration.
Wednesday wasn't the first time Greinke was calling out his pitches. He did the same when he started in Oakland on Aug. 7.
Whatever he is doing, though, seems to be working.
The Astros have the day off Thursday before opening a three-game series against Seattle. The Astros haven't announced their rotation for that series.
The Associated Press contributed to this report.