Chris Brown Grinds on Summer Walker During Steamy Onstage Performance

Chris Brown turned his Saturday night concert into a PG-13 spectacle ... pulling Summer Walker onstage for a steamy performance that had fans losing their minds.

The singer was in Las Vegas for his "Breezy Bowl XX" tour stop when he brought Walker up from the crowd and made her the star of his "Take You Down" number. Walker was ushered into a chair while Brown serenaded her with his slow jam ... and things quickly escalated.

Breezy danced around her, belting out lyrics while showing off his trademark moves. But as the song built up, he mounted Summer and grinded all over her, locking into steamy choreography. The crowd went wild and Summer looked like she was enjoying every second.

Summer laughed through the moment and even fanned herself as Chris grinded up on her ... clearly playing along with the wild scene. The crowd went nuts and she looked like she was enjoying every second.

To cap it off, Brown leaned in for a kiss at the end of the track though the house lights dimmed just in time, leaving fans guessing whether their lips actually met.