Matt McGahan missed the conversion and two kickable penalties to the Steamers relief, as Harbour dominated the opening 20 minutes on the back of six successive penalties awarded and a wealth of possession.
Steamers openside Johan Bardoul impressed in the early stages with some driving runs and a crucial turnover. Chase Tiatia sparked the first scoring chance for the Steamers as the new winger forced a five metre scrum feed but from the scrum Tiatia spilled the ball with the try line looming.
All Blacks hooker Nathan Harris ran 30 metres down the left touchline to spark another attack that led to a penalty. Steamers took the lineout option and halfback Papa Wharewera dived over for a try on debut. Nick Evemy hit the post with the conversion.
As the halftime hooter sounded Nemani showed some more of his attacking skills to regather a chip kick. From the next ruck a penalty was awarded which Evemy slotted to give the Steamers an 8-5 lead at the break.
Halfback Te Aihe Toma, in his 15th blazer game, and openside flanker Zac Hohneck started the second half for the Steamers. Bardoul spilled the ball in a promising position as the Steamers went onto the attack early.
Toma took a quick tap from a handy penalty, Evemy made a clean break, Harris followed up but a try went begging as the ball slipped out of the hooker's grasp. The Steamers had nothing to show from 15 minutes of dominance but Tiatia finally made Harbour pay with a decisive break to score from Evemy's slick pass. Evemy converted to open up a 15-5 lead after 57 minutes.
Ill-discipline from the Steamers gave Daniel Halangahu a chance to kick two penalties to close the gap to 15-11 with 15 minutes to play. The Steamers had a royal chance to crash over from a lineout drive but Nemani joined the maul illegally for a crucial try to go begging.
Harbour refused to give in and when replacement hooker Joe Royal took too long to throw to a defensive lineout, they had their opportunity. Phase play followed and yet another penalty, which Harbour turned into a lineout drive five metres out. But they were thwarted by Troy Callender, who held the ball up and turned over possession for a defensive scrum in a match-saving moment.
Evemy, who had a fine game at first-five, cleared well up the touchline as the heavens opened with deluge rain sweeping across Baypark.
Tiatia may have been on debut but he became an instant Steamers legend after he sprinted 55 metres to score the match winner after a fine pop pass from tighthead prop Pingi Tala'apitaga, which came about thanks to a huge hit in midfield from the impressive Lalakei Foketi.
Bay of Plenty Steamers 20 (Chase Tiatia 2, Papa Wharewera tries; Nick Evemy con, pen)
North Harbour 11 (Junior Tofa Va'a try; Daniel Halangahu 2 pens)
In the curtainraiser, Bay of Plenty Development XV lost 19-5 to Counties Manukau Development XV.
