The lovers were in the middle of having sex in their car when they were interrupted by the policeman, a court heard.
The cop then asked the woman to pass a breathalyzer test, Spanish news agency EFE reported on Friday.
The couple's account of events from a night in October 2009 was backed up by the cop's statement.
In this statement, the officer admitted the accused only lost his temper when he asked for his girlfriend to be given the chance to get dressed.
The court heard how the man from Yecla in Murcia approached the policeman who had apprehended them.
He then shouted: "You think you're so special with that uniform on" and punched the cop in the chest before kicking him in the thigh.
The accused was originally sentenced to six months in prison for non-cooperation with police while drunk but the judge opted for a €730 ($940) fine instead.