Philip Mirfin and newcomer Campbell Higgins, a tertiary student from Tauranga, took comfortable singles wins against Mike Smith and Till Bossmann (St Clair) to set up the result.
Jeff Elliotte got one back for St Clair with an easy win over Ken Thomson, and Darryl Paterson battled to a three-set win over Alan de Zwart.
This left St Clair needing to win both doubles or to gain back a set to force a games countback.
However, de Zwart and Higgins beat Smith and Bossmann 6-0, 6-4 to seal the win.
Elliotte and Paterson won the consolation top doubles 6-4, 7-6 to even the rubbers.
With three experienced veterans and a promising junior the depth of the Harbour team proved too daunting.
St Clair reached the final in controversial circumstances after Balmacewen, which clearly led the points table after round-robin play, used a substitute who had not played the required number of regular season matches without seeking dispensation, for the semifinals.
St Clair had used an injured player to comply with the same rule and Balmacewen had won the tie, but the disputed two rubbers were granted to St Clair and gave it a margin.
St Clair women won the final against Balmacewen to maintain an unbeaten record.
Teenagers Sian English and Georgia Hume won both singles against Brittany Wong and Jessie Stevenson, and the doubles were not needed for a result.
Wong had a matchpoint against English, but English had five herself before clinching a third-set tie-break 14-12 in the gathering gloom.
