Green Island pulled off the upset of the season with a stunning 42-10 win against competition leader University.
Harbour was mightily impressive in its 33-10 win against Taieri as well.
Dunedin overpowered an understrength Zingari-Richmond 79-12, and Kaikorai kept its playoff prospects alive with a comfortable 43-21 win against Alhambra-Union.
There is clinical and then there is the display the Harbour pack produced to dispatch Taieri 33-10 at Peter Johnstone Park.
The Hawks are loaded with powerful ball carriers and the pack proved unstoppable when rumbling towards the line.
They dominated the collisions and spent the entire match providing front-foot ball for a terribly spoilt back line.Harbour opened the scoring from a 10m lineout drive. Hooker Sekonaia Pole had the ball tucked away and was driven over.
There was absolutely nothing Taieri could have done to prevent Harbour scoring from that play and its players were soon back defending their line.
This time, prop Giorgio Bower galloped through a gap close to the ruck. Centres Sio Tomkinson and Hemaua Samasoni had featured strongly earlier in the movement and were a handful for the defence.
When Harbour did not have the ball, it turned defence into attack with some bruising tackling.
Lock Joketani Koroi used his strength to hold up the ball and force turnovers. Openside Charles Elton was always there when his side needed a link man and Solomon Pole was immense.
He won a lot of lineout ball for his side and punched the ball up with rare power. He got a second-half try for his effort and was the pick of a thoroughly impressive forward unit.
Taieri was understrength, talisman Josh Casey out with concussion and lock Josh Larsen and halfback Kurt Hammer also unavailable.
That robbed the Eels of some class but their biggest problem was Harbour just did not allow them to get into the game.
Taieri centre Matt Whaanga conjured up a try from about 50m out when he went around his marker, cut back in and scored near the posts.
The Hawks take on Green Island at Watson Park next which is sure to be an amazing show down after their shock win over University.