Joe Thomas -- a former 325-pound NFL offensive lineman -- DOMINATED the "Titan Games" on Monday ... and now he looks like a LEGIT contender to win the whole show!!
The former Cleveland Browns left tackle has dropped 50 pounds since retiring from pro football in 2017 ... and was personally selected by The Rock to compete on the show, going up against other high level athletes.
Well, turns out ... LINEMAN ARE WAY MORE ATHLETIC THAN YOU'D THINK!!
The 35-year-old Thomas started off slow ... narrowly beating out Denver firefighter Matt Chan in the first half of the show.