Seems like Avril Lavigne and Tyga are still gettin' along pretty well after their split ... because the 2 were spotted kicking it at a club in Sin City only weeks after calling it quits.
Avril and Tyga appeared to be in good spirits in pics and video, obtained by TMZ -- we're told Avril performed Saturday with Marshmello at the Encore Beach Club inside Wynn Las Vegas, and Tyga hopped onstage later that night.
We're told the rapper watched Avril's set from his VIP section of the DJ booth ... and she went over to him after her performance, where the two were spotted laughing and smiling together.
The pair eventually left the club together with their posse ... but not before Avril snapped pics with fans while Tyga waited next to them.
TMZ broke the story, sources told us the split was a mutual decision, with both believing the relationship simply ran its course. You'll recall, they went public in March -- a month after she called off her engagement to Mod Sun.
We were told Tyga and Avril were planning on staying friends, and this looks like a prime example.