Al Michaels -- The DUI Mug Shot

Al Michaels cracked a confused sorta half-smile when it came time for the mug shot following his DUI arrest this weekend ... and TMZ has obtained the pic.

We broke the story ... the 68-year-old broadcasting legend was arrested Friday night in Santa Monica when he allegedly made an illegal U-turn in front of a DUI checkpoint.

Michaels was arrested -- and sources tell us his blood-alcohol level was JUUUUST north of the legal limit.

Sources say Michaels couldn't have been nicer during the arrest.