Chris Brown and Karrueche Tran -- Working It Out ... After Nightclub Sweet-Talking Session

Like a cheesy holiday romantic comedy ... Chris Brown and Karrueche Tran flipped their relationship back to "on" -- all because of a run-in on the eve of Christmas Eve.

Sources close to the couple tell us Chris had been trying to reconnect with Karrueche following their nasty public break-up ... but KT wasn't having it until Tuesday night at Playhouse.

We're told they chatted politely inside the nightclub until Chris asked her to go somewhere more private to talk about giving the couples thing another shot.

Karrueche agreed ... and we actually shot them on the way out of the club to go have that convo.

The final nail in the coffin came Thursday when they went to Sean Kingston's "Christmas with the Kingston's" party -- together. Based on this photo ... the talk went well. Again.