Sam Shepard -- One Tequila, Two Tequila ... Busted for DUI

Two shots of tequila is all Sam Shepard drank ... at least that's the story he unsuccessfully told cops before they cuffed him.

The "Bloodline" actor was popped Monday night in Santa Fe, New Mexico outside a restaurant. A security guard called police, saying he feared Shepard was way too drunk to drive.

Shepard tried in vain to drive away, thwarted by an emergency brake he failed to release. That was enough evidence for cops to pull him over, and administer field sobriety tests ... which he failed. Cops say he also refused to blow into the breathalyzer, and that upped the ante.

He was arrested for aggravated DUI, and remains in custody.

Shepard was arrested for DUI back in 2009.