Justin Bieber Topless Mexican Pics with Selena Gomez

12/8/2011 5:15 AM PST

Justin Bieber was smothered by his smokin' hot adult girlfriend Selena Gomez in Mexico yesterday ... and was so impressed by her incredible physique ... he snapped a few pics to capture the moment.

The couple is south of the border for a friend's wedding ... but yesterday, they spent the day taking in some sun at the hotel pool ... because, why not?