Shirtless J.R. Smith made his return Thursday night ... and we all have Baker Mayfield to thank for it -- 'cause the Cavs star WENT CRAZY after the rookie led the Browns to a win!!!
It all went down at FirstEnergy Stadium in Cleveland ... where J.R. had luxury box seats to see the Baker-led Browns finally win a game for the first time since 2016.
You'll remember ... the last time J.R. celebrated a massive Cleveland victory -- he went topless in public for hours ... rockin' no shirt for the entire Cavs' championship parade.