A famous MLB ump says Paul Lo Duca is lying ... claiming he did NOT "open up" the strike zone for a star Mets pitcher who let him borrow a sick '57 Chevy -- and now he's suing.
The pissed-off ump is Joe West -- a baseball legend who's been working MLB games since the '70s.
West is FURIOUS over claims Lo Duca made during an April 18 podcast on The Action Network ... when the ex-Mets catcher accused West of essentially taking bribes from star closer Billy Wagner.
Specifically, Lo Duca said during a game he was catching around 2006 or 2007 against the Phillies .