Johnny Manziel -- Dash Cam of Cop Incident ... 'I'm Sober'

Johnny Manziel insisted he was NOT drunk during a domestic dispute with his girlfriend last week -- though a 911 caller says his GF may have been hammered.

Johnny and Colleen Crowley were arguing on the side of the road on Interstate 90 on Monday when a concerned witness called 911.

The caller told the operator, "It appears that the girl might be intoxicated."

You can hear Manziel in the background talking to Crowley -- "Baby please!"

Moments later he says, "I'm trying to take her home! I'm sober! Please!"

Cops arrived soon later -- you can see an officer walk Johnny away from the car.

You can also hear Crowley tell an officer she's not physically injured. She does sound emotional toward the end of the conversation.