Paul Pierce says the Celtics-Lakers rivalry is officially back on ... with Kyrie Irving playing the Bird/Pierce role -- and LeBron James playing the Magic/Kobe role!!
We got Paul out at LAX this week and, as one of the key players in the historic NBA clash -- he declared to TMZ Sports the two teams can finally have a real tiff again now that Bron's in L.A.
"It's on. It's on," the Celtics legend tells us.