After only three minutes, Josh Bowkett, Ollerton’s top scorer this season, found room on the edge of the area to curl a shot past Selby’s Peter Lawrie.
Selby were awarded a penalty just before the break but Scott Ward’s spot kick was tipped on to the bar by the legs of keeper Gretton.
It proved pivotal as Ollerton extended their lead in the second half in quick-succession. Mark Carter’s powerful header from Lewis Bingham’s delivery made it two on 63 minutes before Brandon Shaw made it three, three minutes later from close range. Bowkett got his second from inside the area with 15 minutes to go but missed the chance to seal a hat-trick when a late penalty was saved.