Sofia Vergara Dan Reynolds

Sofía Vergara & Dan Reynolds' romantic weekend didn't stop with one dinner date ... because we're told they were spotted flirting at a birthday party not long after -- and they gave others in attendance the vibe that they're a couple.

Sources with direct knowledge tell TMZ ... the pair were seen at Doja Cat's 31st birthday party in Los Angeles late Friday night and early Saturday morning.

We're told the two were spotted in the corner of the room talking closely ... while Sofía stunned in a sexy lingerie top.