Marc Anthony -- Turns Two U.S. Marines into Vegas ROCKSTARS

So there he was, partying in Vegas ... when Marc Anthony noticed two U.S. marines hanging out at the Venetian ... and decided he was going to show his appreciation, by treating them to most kick-ass night EVER.

TMZ has confirmed ... Anthony approached the two marines and personally invited them to hang with him at Tao nightclub Thursday night -- hours before Veteran's Day.

We're told Anthony treated the guys like rock stars -- ordering bottles of expensive booze at a private V.I.P. table and making sure everyone knew they were the guests of honor that night.