If you didn’t know — Pete Crow-Armstrong is fast.

And you saw it on display Wednesday night in San Francisco.

The Cubs rookie scored from first base on a Miguel Amaya single. Yes, you read that right, a single.

With two outs in the 4th inning, Crow-Armstrong drew a walk to keep the frame alive. Then, Miguel Amaya followed with a groundball single up the middle that veered into the left-center field gap.

Then it was time to sit back and enjoy watching Crow-Armstrong do what he does best — run. The 22-year-old glided around second base, then had a quick slip but kept cruising towards third. There, third base coach Willie Harris waved him home and he scored standing up and without a throw.

For all of Crow-Armstrong’s prowess on the basepaths, it was the Cubs’ running game that might’ve cost them in Wednesday’s 4-3 loss to the Giants.

[WATCH: Nico Hoerner assesses Cubs at halfway point of season]

The Cubs made three outs on the bases on Wednesday. Christopher Morel was thrown out at second trying to extend a single into a double in the 4th inning, then thrown out at first in the 6th on a backpick by catcher Patrick Bailey. Then, in the 8th, trailing by a run with Ian Happ at second base and Morel at first, the duo attempted a double steal, but Giants’ pitcher Tyler Rogers picked him off at third base.

[WATCH: Craig Counsell address double steal call in 8th inning of loss to Giants]

Just moments before Crow-Armstrong’s baserunning prowess, play-by-play broadcaster Jon “Boog” Sciambi and Jim Deshaies were discussing how manager Craig Counsell uses the word “unstoppable” when talking about Crow-Armstrong’s speed on the bases.

Crow-Armstrong taught everyone that lesson.