Harwich started brightly with Jack Milne's well-directed low shot forcing the Holland goalkeeper to pull off a diving save, pushing the ball to safety.
The Shrimpers took the lead in the 20th minute with a perfectly placed low drive from Archie Rogers-Bell, which this time was too good for the diving keeper.
Harwich came close again 3 minutes later when Alex Pryke's dangerous in-swinging corner kick hit the crossbar before bouncing down to be cleared.
Holland defended well and half-time came with the Shrimpers leading by the only goal.
Five minutes after the break Harwich increased their lead with Milne (pictured) making no mistake with a clinical finish.
Substitute Harry Hosking came on to make his mark when he drew the keeper out and, from a wide angle, fired his shot into the far corner of the net.
With 15 minutes to go Holland broke through the Harwich defence but goalkeeper Jack Lines kept a clean sheet by making an excellent point-blank stop.
Harwich were soon back on the attack with Kobe Ayling's clever chipped cross being headed inches over by Rogers-Bell.
Before the final whistle, Hosking iced the cake for Harwich by scoring their 4th goal and his second with another good finish.
Harwich team: Jack Lines, Luca Sayer, Riley Stevenson-Miller, Theo Stevenson-Miller, Rob Pratt, Ewan Livingston, Alex Pryke, Archie Rogers-Bell, Cody Harrison, Jack Milne and Joshua Beavis. Substitutes: Samuel Hockey, Alfie Behn, Kobe Ayling, Harry Hosking and Kristian Skeggs.