City striker Jamie Devitt matched McCormack by also scoring three on the night but his efforts were in vain.
Club skipper Richard Naylor played a full 90 minutes in his comeback after injury and Sanchez Watt completed 85 minutes on his return from injury.
Scottish international McCormack's first goal was scored from close range just before half-time as United went in 3-2 at the break.
His second was a stunning free-kick soon after half-time and, after he had hit the woodwork, he completed his hat-trick by finishing off a pass from left-back Ben Parker.
Neil Redfearn was in charge for the first time following Neil Thompson's sudden departure last week.