Miss Arizona Teen USA Tori Vance -- Okay Fine, I Was BUZZED Before DUI Arrest

Former Miss Arizona Teen USA Tori Vance -- who pled "not guilty" to DUI last week after her recent arrest -- is now admitting ... she DID have something to drink before cops busted her behind the wheel last month.

Tori was out shopping in L.A. yesterday with a beauty pageant buddy when she gave us the blow-by-blow -- saying, "I was coming from Rosa Mexicana. It was Cinco de Mayo. So I shouldn't have been driving. I know better."

Tori added, "I didn't even give it a thought and I had something to drink."

QUICK REMINDER -- TORI IS ONLY 18 YEARS OLD.

After leaving the restaurant, Tori said she pulled an illegal U-turn and -- just her luck -- a cop car was right behind her. The giant sombrero she was wearing at the time probably didn't help her case.