The songstress and her baby daddy were raging Friday night after hitting the town on the East Coast to ring A$AP's 35th born day ... which was actually on Oct. 3. Nothing like a prolonged party though -- and that's exactly what RiRi and AR had on their hands here.

It appears to have been an adult-only rager ... sans any sign of their 2 little ones. As far as where exactly they were -- apparently, they started in the Big Apple, and made their way to a go-kart joint in Jersey City after -- though, unclear if that's where this shindig went down.

In any case ... they were living it up big time, dancing up on each other and boogeying on down with their close friends nearby. Rihanna, specifically, made sure to bust out the moves.

We must say, post-delivery of her 2nd son in August -- she's looking pretty damn good ... and about as spry as ever. And dare we say ... she's still hot as hell, despite what Drizzy might be claiming now.

Of course, we're referring to the shots he took in his new song 'Fear Of Heights' -- where he lamented the fact people felt he hadn't moved past RiRi ... while also claiming he'd been with way hotter women than her -- and also, he suggested A$AP was "stuck" with Rihanna.

In the wake of his latest dig at his ex ... Drake's been getting dragged across the coals by Rihanna fans -- who were quick to point out how obsessed home boy was back in the day. Remember, he infamously declared his love for her on live TV during the 2016 VMAs.

They actually dated for a bit after that ... but it didn't last, and the relationship fizzled.

A couple years later, Rihanna kinda shaded Drake in a Vogue cover story ... saying this about the status of their relationship, "We don’t have a friendship now, but we’re not enemies either. It is what it is." The outlet also noted her "eyes glaze[d] over with cool indifference."

She hasn't talked much about him since, but Drizzy's still going on about her ... a mom of 2, who's in a committed relationship ... and who's billionaire fashion mogul.