Carrie's been denying their romance, but the lips don't lie!

Carrie Underwood helps Dallas Cowboys quarterback Tony Romo ring in a memorable birthday celebration Saturday at Ghostbar in Dallas.An insider says the Idol champ and Romo were "laughing, singing together, holding hands and their arms were around each other all night."

So are they a couple? "They have recently been spending a little time together," Underwood's rep tells People, adding, "It's [in the] really early stages."