A serial sex fiend pleaded guilty Wednesday to the rape of a Long Island student in the bathroom stall of a Flatiron District bar, in a deal giving him 20 years-to-life in prison.

Rodney Stover, 49, copped to three counts of predatory sexual assault for the April 11, 2015, attack at the Turnmill Bar, where the victim, 23, and her boyfriend were celebrating a pal’s birthday.

After the rape, Stover fled but was caught a few days later when bar staffers saw him lurking in the neighborhood, cops said.

Stover had just left prison in February 2015 after serving a 20-year stint for raping a woman in Southampton and another in Pittsburgh.