P.J. Williams' GF tried like hell to get the NFL player out of a DUI arrest last January ... asking a cop if he'd have mercy on P.J. because of the missed PI call in the Saints-Rams NFC Championship Game!!!
It's all in new police video obtained by TMZ Sports ... which shows a New Orleans cop stopping Williams after he pulled the guy over for doing 80 MPH in a 50 just days after New Orleans' loss to L.A.
The cop tells P.J. he was driving recklessly ... and after he says he smells a strong booze odor from the car -- he decides to conduct a sobriety test on the 26-year-old.