Michael B. Jordan -- 1st Pics As Apollo Creed's Grandson ... In New 'Rocky' Flick

Apparently, patriotic trunks run in the family -- 'cause Michael B. Jordan was sporting Apollo Creed's famous shorts when he stepped in the ring to play A.C.'s grandson in the new "Rocky" flick ... and TMZ Sports has the 1st pics.

Jordan was going toe-to-toe with real-life pro boxer Tony Bellew -- who plays a boxer named "Pretty Ricky" in the upcoming movie.

The pics were taken on February 26th ... just a few days before hell broke loose on the set -- with Sylvester Stallone jumping in the ring to break up a REAL BRAWL that went down between Bellew and an actor playing one of his corner men.

Reps for the studio tell us the fight never got physical -- multiple witnesses tell us otherwise.

As for Apollo Creed himself ... he died in "Rocky IV."

Sucks for Carl Weathers.