With both teams in mid-table, a close contest was expected and the first half was evenly contested.
The Shrimpers' first chance came when Jenson Goode crossed and Oakley McNair headed the ball back across the goal for Louie Bloom's header to go just outside the post.
Ilford also created a good opportunity, culminating with a shot that was also just off target.
Harwich's Alfie Canning also saw a headed chance go just past the upright.
Ilford took the lead when a pass was intercepted by Mohamed Habib, who beat his marker before cutting inside and cleverly using a second defender as a shield for his hooked shot into the far corner of the net, giving Shrimpers goalkeeper Will Healy no chance of saving.
Harwich came out for the second half looking to get back on terms and were pressing when, in the 60th minute, their striker Joe Knight was sent off.
Ilford were pacy in attack and Daniel Izekor fired in a fierce drive that fizzed just over the crossbar and their wingman Shaike Kamara's later had a cross-shot strike the post.

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Harwich's 10 men were holding their own and from a well-placed Goode free kick, McNair's header was just off target.
With 25 minutes remaining, Harwich had got on top and Bloom, now leading the attack, did exceptionally well to win the ball and hold off a determined challenge before goalkeeper Ben Szubski came off his line to save a goal-bound shot with his feet.
Bloom (pictured) was everywhere, giving the visiting defence a testing time, and he broke through again, but with the ball difficult to control, his lob cleared the crossbar.
Harwich pounded the Ilford defence in the closing 15 minutes, with Rory Harman's dangerous cross forcing Szubski to make an excellent save by turning the ball over the crossbar.
Ilford put their bodies on the line to survive the onslaught that had the 183 supporters on their toes until the final whistle.
Harwich team: Will Healy, Rory Harman, Charlie Canham, Oakley McNair, Jeremiah Ajisafe, Jenson Goode, Alfie Canning, Alfie Eldridge, Louie Bloom, Tiwa Odufuye and Joe Knight. Substitutes: Josh Hawkins, Tobi Dehinsilu, Omari Obwoya and Liam White (all used).