It was just reward for Hailemariam after minutes earlier passing a gift ball to Cam Vickers who had slipped and fallen as the ball went begging past him from a dangerous position at the top edge of the box.
However, another tireless worker for the hosts, Tom Biss, scored the equaliser, 1-1, a minute before halftime to send both sides back to the drawing board.
It was fellow Blues striker Saul Halpin who pounced on the ball on the left flank after Canaries defender James Gray slipped to cough up possession inside the box.
Halpin put a crisp ball to an unmarked Biss across the face of the goalmouth for a tap-in goal.
Midway through the first spell, Lower Hutt goalkeeper Reed Collingwood almost conceded a goal when he slipped while clearing a ball fed back to him from a defender but the gloveman caught enough of the ball with his foot to curl it away from harm's way.
The Park Island pitch, bathed in sunshine, looked sublime after a white-out blanket frost that saw the day start in minus-degree temperatures although there was a hint of stubborn dew that might have created some cleat-traction issues for players.
The Rovers had two key players on the bench, including skipper/centreback Danny Wilson and midfielder Ryan Tinsley, after a 3-1 loss to Stop Out last Saturday.
Teenage midfielder Ross Willox made his starting debut for the Blues with Finlay Milne slipping on the skipper's armband for the first time.
However, whatever player/coach Bill Robertson and assistant coach Chris Greatholder said in the changing rooms the hosts returned to the park with some intention.
Angus Kilkolly struck in just the first minute of the second spell when he nodded in a header from a Halpin cornerkick to make it 2-1.
Midfielder Josh Stevenson made it 3-1 in the 52nd minute after curling in a rip-snorter of a ball from 30m out with a peraler of a left-footer from dead centre of the field to leave keeper Collingwood bewildered.
Tinsley came in for Willox in the 60th minute although the 17-year-old had made a calm-and-composed contribution while on the park.
Harry Morton, back from his American university commitments late on Thursday night, came in for Kilkolly in the 66th minute.
However, it was Haillemariam who pulled a goal back again, 3-2, a minute later when he received a through ball, beat Baxter in the race for the ball, stayed on his feet in the one-on-one contact before zipping around the keeper to deposit the ball into an empty net.
But Rovers weren't done. In the 72nd minute Halpin showed some of his wizardry near the left upright, bamboozling defenders before jabbing the ball back 45 degrees to Stevenson to claim his second goal, 4-2, with a point-blank header.
In the 82nd minute, Wilson replaced James Hoyle at centreback.
Three minutes later, referee Mark Whitehead ran almost the length of the field to Canaries keeper Collingwood to flash a yellow card for what appeared to be abuse.
The Blues could have scored a few more but Lower Hutt would have gone away feeling they did enough to keep fans entertained.
It's the Chatham Cup opener for the hosts in another 2pm kick off here on Monday.
