He went from hero to zero in a few boozy hours.

Shortly after NYPD Officer Eugene Donnelly donned his dress blues for a medal ceremony at One Police Plaza, the cockeyed cop sported only his underwear when found in a stranger's Bronx apartment.

The polluted policeman, a four-year veteran, allegedly roughed up the female resident during the June 10 bender — and officials say he was too blotto to recognize his whereabouts.

"He was apparently drinking," a police source told the Daily News of Donnelly. "He was celebrating. He went to stay with a friend."