A misjudgement within the first few minutes allowed Nik Zlatev a clear run on goal and he slotted the ball past advancing goalkeeper Brad Cook for Basildon's first goal.
Cook then saved Harwich from going further behind with an acrobatic leap to turn a goalbound shot over the crossbar.
Harwich were under constant pressure with the ball coming back at them from their defensive clearances. It was not until the 20th minute that the Shrimpers had a shot on goal when Zachary Pedro broke through United's defence.
Basildon were quicker to the ball, playing neat passing football, whilst Harwich were not finding their men. The Shrimpers' only other scoring chance of the half came when Luke Mayhew (pictured) sent over a dangerous cross and in a goalmouth melee the ball fell kindly for the United defence to clear.
Half time came and Basildon's superiority was such that Harwich were thankful to be only 1-0 in arrears.
In the 60th minute, Harwich lost the ball in defence, allowing Basildon to play a neat one-two with Zlatev scoring his second goal.
Ten minutes later Harwich had their moment of magic with Mayhew sending over the perfect cross for Shaun Avis, at the near post, to reduce the arrears with a brilliantly taken header.
Harwich were now matching Basildon and Alfie Eldridge had a shot well saved by United goalkeeper Enos Duah at the expense of a corner kick.
In the closing 15 minutes, Harwich pressed, seeking an equaliser, with Mayhew prominent on their right flank. It was Mayhew who came the nearest to gaining the point which they sought when, from Tyler Sullivan's assist, his lightning shot from a wide angle was touched onto the crossbar by Duah.
Harwich team: Brad Cook, Tom Watkins, Oakley McNair, Jack Wood, Reece Harte, Alfie Eldridge, Louie Bloom, Alfie Canning, Luke Mayhew, Zachary Pedro and Shaun Avis. Substitutes: Tiwa Odufuye, Tyler Sullivan and Liam White (all used)