Flanker Eben Joubert won the battle at the break-down and played a big hand in Harbour's dominating win over Alhambra-Union at the North Ground.
He was a like terrier the way he hunted the ball at the breakdown which gave Harbour the go-forward ball that its backline used efficiently.
The Harbour forwards operated as a unit, with Jason Kelly joining Joubert to win quick ball at the breakdown.
The front row of Ben Nolan and Pete Mirrielees also did their bit with their driving play and the pick and go.
The Alhambra-Union forwards lacked fire, while the backline turned over so much ball that attacking moves seldom got past the first phase.
Big Harbour centre Siaosi Folau, who made some strong breaks through the centre, scored the first try after 12 minutes when he broke the defence close to the line.
Aaron Bancroft always looked dangerous in the midfield and put the game out of Alhambra-Union's reach when he ran in at speed to collect loose ball at halfway and ran away for the third Harbour try after six minutes in the second spell.
Paul Archbold was the best Alhambra-Union back with his pace on the counter-attack.
He was unlucky not to score a try after a 70m run and kick ahead in the first spell.
Harbour scored two tries in the first spell to lead 18-3 at the breakdown and then held its composure to retain its lead.
Harbour 25 (Siaosi Folau, Aaron Bancroft, Pete Mirrielees tries; Johnny Hughes 2 conversions, 2 penalty goals), Alhambra-Union 14 (Jone Paumau try; Peter Breen 3 penalty goals).
Half-time: Harbour 18-3.
Referee: Tim Baker.
