Drake Whipped by Rihanna ... and Her Booty

Drake got way more than weak in the knees for Rihanna during her concert -- he got all up in her kitchen, and the fans LOVED it.

He joined her onstage in Manchester for their "Work" duet, and even though they've flirted onstage before ... Drizzy seemed to take it a little further this time with an actual kiss on RiRi's neck.

There are always rumors they're getting back together, and his laser focus on her ass in this clip explains why. He even gushed about her when the song was over.