The Hawks were on top in the first half but unable to convert their chances, before the game opened up into a thrilling second half.
Junior Dadson converted a close range finish to take the lead and despite the visitors rallying late in the game, the Hawks were good value for their win that moved them two places up the league table.
Harlow Town were on the front foot from the whistle, and could have gone ahead within the first two minutes. A deep cross from Jimmy Shepherd found Junior Dadson, but his side-footed shot was cleared off the line.
Jared Small tried his luck from distance with low shots that just went wide of the post, before Syrus Gordon saw his effort tipped around the post as the Hawks controlled the opening exchanges.
Gordon went close again when Alex Read cut back for the midfielder, but Leiston stopper Marcus Garnham parried the shot and then dived on the loose ball to prevent the follow-up.
The visitors were struggling to offer anything in attack, and when Regan Pelling shot from 35 yards out it went high and wide of the Harlow goal.
The best chance of the half came five minutes from the whistle. Good pressure from Jared Small was rewarded when he stole the ball on the byline. He picked out Alex Read in the middle, but the striker uncharacteristically mistimed the shot and he couldn’t connect from six yards out.
HT: Harlow Town 0-0 Leiston
Leiston came out looking like a different team in the second half and posed a threat straight away. Matt Blake was through on goal but David Hughes, recalled to the squad and only making his second appearance of the season due to injury, saved well at his feet.
Kelsey Trotter picked up the rebound but put it wide to waste a good chance, before sending another effort over the bar from the edge of the area just a minute later.
The visitors were growing into the game, but Harlow still looked to attack at every opportunity as the game ebbed and flowed. A mazy run to the corner of the goal area from Alex Read created space for a shot, and the powerful effort stung the palms of Garnham who got two hands behind it to push it to safety.
At the other end, David Hughes then parried a long distance shot himself, denying Regan Pelling from 25 yards. Hughes then reacted quickly to dive at the feet of Blake and prevent him sweeping in the follow-up.
On 66 minutes the breakthrough game. Alex Read fed the ball into Jared Small, whose smart turn and delivery was on a plate for Junior Dadson at the back post. He volleyed in from close range to take a deserved lead.
The lead was nearly doubled two minutes later. A cut-back from Fabion Simms just needed to be buried by Alex Read six yards from goal, but it was an incredible reaction save from Garnham who somehow managed to get a hand to it.
Garnham saved well again from Junior Dadson on two occasions as the Hawks looked to kill off the game.
With fifteen minutes remaining, the visitors threw everything at it. A corner was cleared to Byron Lawrence, and he unleashed a thunderbolt of a shot that cannoned off the bar.
David Hughes capped an impressive return to the team when Matt Blake broke through the defence late on. He saved down low to his right to preserve his clean sheet and ensure the Hawks took a vital three points to start to climb the league table.
FT: Harlow Town 1-0 Leiston
Harlow moved up two places in the table to 21st place, with 15 points from 16 games.
The attention now turns to the FA Trophy, as Dulwich Hamlet make the trip to the McCullochs Arena. Kick off is 3pm on Saturday 11th November.