This game started at a pace that rarely dropped and in the first five minutes Peterhead could have scored twice.
The inevitable opener came after ten minutes, Simon Ferry slipping a perfectly weighted ball forward to Riley who dinked the ball over Reid and into the net.
The visitors struck again in the 23rd minute. Riley pounced on to a through ball and shot past Reid. After 38 minutes the Blue Toon struck again when Stevenson drilled a shot home from the right side of the penalty area.
Less than five minutes after the restart, a pinpoint through ball by Kevin Dzierzawski split the home defence and McAllister finished with a cute flick in typical Rory fashion.
United pulled a goal back with Stuart Smith heading in a Scott Barbour corner but the four-goal margin was restored after 79 minutes with a sublime effort from Stevenson.
A minute later and with Formartine heads reeling Stevenson did it again this time side-footing his hatrick as the ball was whipped in his direction.