A thug who spun a spree of uptown gunpoint muggings into a murder by crashing his getaway car into an elderly nun in Harlem will serve 18 years to life after pleading guilty yesterday in Manhattan Supreme Court.

Dyson Williams, 22, of Manhattan, had just committed his fifth early-morning mugging two summers ago — by brandishing a gun at pedestrians and swiping their cellphones and bags — when cops pulled his car over at West 142nd Street.

Williams zoomed away and struck a group of pedestrians. Sister Mary Celine Graham, 84, died, and four others were injured.