An eyewitness tells ET the two arrived together to Drai's Nighclub at The Cromwell, where the "Na Na" singer -- a resident artist at the club -- was performing.
Kardashian watched Songz (real name: Tremaine Aldon Neverson) from a VIP booth next to the stage, smiling the entire night, which is extremely impressive seeing as he was surrounded by scantily clad dancers during parts of his set.
The source tells ET the pair were spotted making out in the early morning hours, after they moved on to Drai's After Hours nightclub. "They weren't shy about it!" the eyewitness said.
The reality TV star didn't share any photos or videos from her night out in Sin City, but a few hours earlier, she did share a sultry selfie showing off her very long blonde locks and plump pout on Instagram.
"The most annoying thing about tabloid rumors is the double standard," she wrote. "If I'm 'spotted' hanging with a guy at a party -- even if I'm just saying hi for a quick second -- it immediately becomes a negative headline about how many guys I'm dating or how I'm getting into a new relationship. Men don't get that reputation! They get a pat on the back. It irritates me."
Kardashian explained that photos taken of her are just "moments in time," not proof that she’s with someone or on more than a first date with a new guy. She also noted "that kind of gossip affects how people see me," which makes dating very difficult. "A guy could assume I'm dating someone and not approach me, when I'm actually single," she said.
Kardashian most recently dated NBA pro James Harden, with the two calling it off in February after first stepping out together in October 2015. In May, she filed for divorce from her estranged husband, Lamar Odom, for a second time. The two are reportedly on good terms, with Kardashian having originally put the proceedings on hold as she helped him recover from health issues following his being found unresponsive at a brothel in Nevada last October.
Watch the video below to hear more about the Keeping Up With the Kardashian star's dating frustrations.
Reporting by Brendon Geoffrion.