Its forwards withstood the battering from a powerful Pirates pack and the backline displayed class in the early semifinal at Carisbrook.
Harbour also made the final with an upset 19-18 win over Southern in the other semifinal.
Just three years ago, Taieri was playing premier two rugby and gained promotion by beating University B 42-17 in the promotion-relegation game.
The following year it finished eighth in the premier competition and moved up to fifth last year.
The club has rejuvenated Dunedin club rugby with its constructive style of rugby and its huge support base. Two busloads of supporters crowded into Carisbrook for the semifinals and others came in cars.
Harbour also has a big support base and there was an estimated crowd of 2500 at Carisbrook on Saturday.
Harbour's win was also impressive because it had been beaten 52-5 by Southern seven weeks ago.
It had to win its last five round-robin games with bonus points to make the semifinal.
• The Taieri pack stood up to a battering from the Pirates forwards to pave the way for a comfortable win in the early semifinal.
Taieri got on top early and scored two tries to lead 18-3 after 26 minutes.
Lock Matt Larson had a powerful game, dominating the lineout and making seven clean takes.
The first try, after 19 minutes, came from a Larson take. First five-eighth Ben Nowell broke through and Kieran Moffat was in support to score the try.
Winger Matt O'Sullivan scored the next try when the ball came loose at halfway. He booted it downfield and won the race to the line.
The game changed when former All Black Paul Miller came on at No 8 and Pirates exerted pressure with battering ram tactics. Miller was backed by hooker Shaun McCarroll and flanker Daniel Crichton.
Taieri led 18-6 at the break but spent the first 13 minutes of the second spell camped inside its own 22m as Pirates hammered the line.
The game changed when lock Kurt Webster made a try-saving tackle and Taieri regained the initiative.
Two quick tries midway through the spell took the game out of the reach of Pirates. Nowell scored a try after a 5m scrum, and Moffat scored his second try after a kick ahead by reserve halfback Ryan Hammer was gathered by hooker Will Hurst and Moffat ran 35m to the line.
Moffat and Nowell were the key players in the Taieri backline and No 8 Charlie O'Connell, Hurst, flanker Nathan Young and Larson and Webster were dominant in the forwards.
Halfback Stephen Bruce was the best of the Pirates backs.
- Taieri 28 (Kieran Moffat 2, Matt O'Sullivan, Ben Nowell tries; Nowell con, 2 pen), Pirates 11 (Daniel Crichton try; Ben Miller 2 pen). Halftime: Taieri 18-6. Referee: Ben O'Keefe.
• Harbour won a nail-biter when Tony Fenner's drop goal attempt swung 50cm wide of the posts.
The fullback's goal kicking and some ferocious close-quarter defence had kept Southern in the game when the Harbour pack was in dominant mood in the last 60 minutes.
Fenner put his team in the box seat by kicking four penalties in the first 22 minutes to give Southern a 12-6 lead at the break. He finished with six penalties from his seven attempts, and his miss hit the posts.
Southern still had the chance to win the game when the forwards charged upfield with the pick and go in the final minutes. They kept hold of the ball for the last four minutes in an attempt to get a penalty.
When that did not come, Fenner stepped back into the box, eyed the posts and let fly with a drop goal attempt in the final seconds.
Harbour was almost penalised out of the game until it adjusted to the referees' calls midway through the first spell.
Harbour fullback Craig Sneddon closed the gap with two penalties, and a try should have been scored when he broke up the grandstand touch. But he kicked ahead instead of passing to an unmarked man on his right.
The Harbour pack exerted pressure throughout the second spell and camped inside the Southern 22m for long periods.
The only try of the game came after five minutes when Harbour exerted sustained pressure and winger George Folau crashed over after six phases.
Another try was denied midway through the spell when Harbour spent five minutes hammering the line. No 8 Ra Kahakiwa knocked the ball on when diving for the line.
Harbour took the lead for the first time after 24 minutes when Sneddon drop kicked a 43m goal from the sideline.
The front row of Pieter van der Merwe, Peter Mirrielees and Ben Nolan laid the foundation for Harbour's win.
They were backed by Sam Ready, who made six clean takes in the lineout, and flanker Angus Duckett, who was a terrier at the breakdown and with his marauding tactics.
The backs defended stoutly, with midfielders Lex Kaleca and Corey Kara and winger Folau forming a rock-like defence.
The best Southern forwards were No 8 Andrew Stead, flanker Sam Crompton and lock Tom Franklin. Fenner, second five-eighth Luke Herden and the inside pairing of Robbie Smith and Julius Glasson were the best of the backs.
- Harbour 19 (George Folau try; Craig Sneddon con, 3 pen, drop goal), Southern 18 (Tony Fenner 6 pen). Halftime: Southern 12-6. Referee: Liam Scanlon.