Hackney Wick started well, causing Harwich problems with their quick breaks and after 20 minutes won two free kicks on the edge of the Shrimpers penalty area.
Harwich managed to clear the first of these but from the second Adam Chenti shot low into the corner of the net to give Hackney the lead.
Shrimpers goalkeeper Brad Cook was having a busy afternoon and 5 minutes later he made a good save to prevent the home side going further ahead.
With 30 minutes gone, Harwich produced their first dangerous attack when they won a corner kick which resulted in a goalmouth scramble that Hackney Wick somehow managed to clear.
Another Harwich corner found Louie Bloom who rifled in an excellent equaliser from 20 yards.
Harwich's joy was short lived as, in the 40th minute, Chenti pounced on a loose clearance and restored Hackney Wick's lead.
Then, with half time imminent, the referee deemed that Alfie Eldridge (pictured) had fouled his opponent and that this was a red card goalscoring-denial offence.
Hackney Wick had been the better team but Harwich came out for the second half determined to make a fight of it. However, with 58 minutes gone the Shrimpers suffered another setback when an error let in Leo Pola who made the score 3-1 in Hackney Wick's favour.
Harwich's hopes of a surprise comeback were dashed when in the 70th minute Pola netted again with a neat header.
The Shrimpers had opportunities to reduce the arrears with Zac Pedro making a good run and later Bloom working a shooting chance, but with 5 minutes remaining Chenti completed his hat-trick for the impressive Hackney Wick team.
Harwich team: Brad Cook, Alfie Eldridge, Tiwa Odufuye, Charlie Canham, Jack Wood, Tyler Sullivan, Gareth Heath, Luke Mayhew, Zac Pedro, Louie Bloom, Shaun Avis. Subs: Oakley McNair, Freddy Cooper, Jack Milne (all used), John Watkins (not used).