Report by Daniel Rogers
After 3 minutes' play Danny Garrad beat the offside trap and forced Rovers goalkeeper Alex Archer to save low at the near post.
Harwich were on top in this opening spell and forced a succession of corners without being able to make them tell.
Following great link-up play with fellow striker Louie Bloom, Garrad again tested Archer with a shot.
With the midway stage of the first half reached, the match had developed into a good contest with both teams up for the challenge.
Haverhill made a quick attacking break and Shrimpers goalkeeper Brad Cook pulled off a super save at his near post.
With 37 minutes gone, Cook was in action again with a top-class save from a 20-yard free kick which was heading into the top corner of the net.
A couple of minutes before the interval Garrad sent over a great cross which Bloom was inches away from netting and the teams went in with an entertaining match still goalless.
Soon after the restart, Rovers failed to clear their lines and had a narrow escape when Bloom's effort hit the outside of the goal post.
Harwich took the lead in the 52nd minute when Liam Riley sent over an excellent corner kick for Charlie Canham to head home.
Sixteen minutes later, Rovers equalised when the Shrimpers defence failed to clear a corner kick and Seymour was left with a tap-in goal.
In the 75th minute, Harwich regained the lead with the best goal of the game. Following lovely link-up play with Liam White, Bloom's cool finish from 15 yards was sublime.
Harwich strove for the clinching goal with Garrad having a shot cleared off the goal-line and then, in the 85th minute, came within inches of scoring when Archer tipped Alfie Canning's free kick onto the post. A minute later Archer produced another good stop when Harwich's impressive defender Jack Wood (pictured) joined the attack.
With a minute of normal time left, Seymour scored his second close-range goal to salvage a point for Rovers and keep the teams in a neck-and-neck race with Stanway Pegasus at the top of the league table.
Harwich team: Brad Cook, Keelan Milburn, Jack Wood, Charlie Canham, Reece Harte, Alfie Smith, Brad James, Liam Riley, Alfie Canning, Danny Garrad and Louie Bloom. Substitutes: Liam White, Alfie Eldridge, Greg Rodger, Dan Keeble (all used), Harry Tuck (not used)