Andre Berto -- Lil Za Would Kick Justin Bieber's Ass ... In The Boxing Ring

There's finally a place Lil Za can say he's better than Justin Bieber ... the boxing ring ... 'cause Andre Berto tells TMZ Sports Za would DOMINATE the Biebs if the two laced 'em up.

Bieber's dabbled around in the squared circle recently, training with his pal Floyd Mayweather in the pugilistic arts ... and posting the videos to social media for everyone to see his skills.

Za one upped the Biebs this past weekend ... actually stepping in the ring FOR REAL and winning his first amateur fight at a college fight night in L.A.

We spoke to Berto, who trained Lil Za for his fight -- and he says that he's seen Bieber's skills and right now Za would have a clear edge.

"Lil Za would edge him out in the ring. He's been training a lot more than Justin and that comes into play."

Fear not Beliebers ... Berto says that if JB showed the same dedication to the sport that Za has, things could definitely change 'cause in his expert opinion, Justin's got the goods.

"Justin is bigger and he is pretty quick, but Lil Za puts in the time and training."

Soooo ... after Mayweather/Pacquiao then?