Partying at Jewel nightclub at ARIA Resort & Casino, the rappers were seen getting "a little flirtatious," says a source.
As the newly single star performed a few of her hits, Montana – who arrived at the hot spot shortly after Azalea – "bopped his head, but didn't seem to really know the songs," adds the source.
Along with the rest of their group, the duo left the club together after 2 a.m.
One day before her club outing, Azalea posted a sexy mirror shot of her backside, simply captioning the photo "#Vegas."
"I broke up with Nick because I found out he had brought other women into our home while I was away and caught them on the security footage," she wrote on Twitter in June.
Earlier this month, Young confirmed he is expecting a second child with his girlfriend Keonna Green.