The Hawks lined up with familiar faces alongside new signings and triallists, but it was an old hand that broke the deadlock when Fabion Simms received the ball on the edge of the area. His neat lofted finish went over the keeper's outstretched hands.
Harlow had the better of the first half, with David Cowley and Alex Read both hitting the woodwork, while Harry Prince was working well on the right wing.
The visitors hit back early in the second half when a Newmarket striker put the ball between the legs of goalkeeper James Hassel. The old Harlow favourite was turning out for the club several years after he last pulled on the number one shirt.
Several substitutions in the second period saw Junior Dadson and Robbie Martin take to the field, while George Smith and Ben Hart also featured.
A sublime goal from David Cowley settled the tie, when a cross from Dadson fell to Cowley 25 yards out. He turned and rifled a left-footed shot goalwards giving the 'keeper no chance.
The Hawks are next in action on Saturday 11th July, in the Joma Challenge Cup in Memory of Jack Chapman. The day will consist of a youth tournament, followed by the next pre-season friendly against King's Lynn.