Harbour took about 60 minutes to grind Pirates down at Watson Park.
It used its big forward pack to bash the ball up and eventually the gaps started opening up.
Pirates defence held for about three quarters of the game before fatigue set in.
The home side opened the scoring with a penalty, but the game took a while to settle into a pattern. Centre Aleki Morris made a half break and Sekonaia Pole got the ball on the 22m and sprinted around under the posts to score the game’s opening try.
Winger Jerome Harimate scored three minutes later in the corner after some sustained pressure.
Will Scorgie pegged the score back with an intercept try for Pirates and his side went into the break trailing 19-10.
Harbour struck first in the second spell with Morris going over after another nice build-up. But you cannot keep Pirates loosie Josh Clark out of the action for long. After four or five phases, he burst through the line and scored close to the posts.
Pirates were spent, though, and Harbour dominated the next 15 minutes, scoring three tries to clear out and eventually win 45-24.
Charles Elton and Hale T-Pole had strong games for Harbour, while Harimate was hard to pin down.
Pirates first five-eighth Craig Sneddon had the last say. Scorgie swooped on some loose ball and flicked it up to Sneddon who raced away to dot down under the sticks.