Hamm -- easily one of the biggest Cards superfans on the planet -- had a front row seat for St. Louis' 5-2 win over Bateman's Dodgers on Tuesday ... and he made sure J.B. never heard the end of it.

The Dodgers are currently in a tight race for the playoffs ... but have lost 7 of their last 10 games (which might explain why Bateman looks like he just saw a dog get hit by a car).

It wasn't all sadness for Bateman, though ... at least he got to see Manny Machado hit a dinger.