Dunedin and University A have virtually confirmed the other two spots, and the battle between them is for third place.
Taieri leads the Gallaway Trophy competition with 73 points and is followed by Southern 62, University A 54, Dunedin 54, Harbour 48, Alhambra-Union 41, Kaikorai 38, Zingari-Richmond 33, Green Island and Pirates 6.
Harbour lost its chance of making the top four when it was beaten 19-16 by Taieri. Its five-game winning streak came to an end, and it is now six points adrift.
Taieri 19
Harbour 16
A final-quarter scoring blitz saw Taieri retain the Challenge Shield in the Henderson Memorial match at Peter Johnstone Park.
Both sides brought intensity and urgency into what was a must-win game for Harbour's semifinal aspirations.
For the first 60 minutes, Harbour enjoyed a wealth of territory and possession, only to be undone by handling errors and a high penalty count.
Taieri halfback Kurt Hammer broke the game open with a run from a breakdown in midfield, his offload putting first five-eighth Josh Casey into space to score the try.
Casey's conversion and a penalty just two minutes later gave Taieri a handy 16-9 lead. But Harbour regrouped, and its all-out assault resulted in a try to fullback Mateo Malupo. The conversion made it 16-16, but Taieri regained the lead through Casey when Harbour infringed shortly after the restart.
Casey's effort in scoring all Taieri's points followed some excellent work from the Taieri pack, which had to scrap for every inch of territory and ounce of possession.
Loose forwards Alex Fitzgerald, James Lentjes and Willis Scott complemented a tight five kept honest by a Harbour pack under the inspirational leadership of captain Peter Mirrielees.
Both sides produced some superb covering play out wide, which contributed to the low score.
Taieri 19 (Josh Casey try; Casey con, 4 pen), Harbour 16 (Mateo Malupo try; Oliver Cuthill con, 3 pen). Halftime: Harbour 9-3.
Southern 31
Alhambra-Union 22
The return of counter-attacking fullback Bryce Hosie added punch to the Southern backline and led to a comfortable win over Alhambra-Union at Bathgate Park.
Hosie kicked six goals from his eight attempts and used his pace to score an early try, finishing with 21 points.
Southern took the game by storm from the start. Hosie kicked a penalty goal after three minutes, and two minutes later used his speed down the right flank to score a try.
The first half was played at pace, with both sides scoring two tries, and scores were locked at 15-15 at the break.
Southern's rush defence in the second half made it difficult for Alhambra-Union to break out and get beyond the advantage line.
Controlled play by Southern forced Alhambra-Union to make mistakes, and Hosie kicked three more penalties.
When winger Byron Dodge scored after 23 minutes, Southern had scored 16 unanswered points and led 31-15.
Strong running and rugged defence by second five-eighth Tei Walden kept the pressure on Alhambra-Union.
In the Southern forwards, No 8 Lafaele Faamoe made ground with the ball in hand, flanker Josh Tye was a useful link player, and Adam Knight made six two-handed takes in the lineout.
Caleb Gray and Peter Breen were the best Alhambra-Union backs, while Scott Manson and Liam Coltman were strong in the front row. They were both skilled in the pick and go, and Coltman snaffled a lot of ball at the breakdown.
Lock Mike Colville made nine clean lineout takes, including two off Southern throws.
Southern 31 (Bryce Hosie, Nathan Cargo, Byron Dodge tries; Hosie 2 con, 4 pen), Alhambra-Union 22 (Jason Emery, Peter Breen, Liam Coltman tries; Breen 2 con, pen). Halftime 15-15.
Zingari-Richmond 27
Kaikorai 21
Zingari-Richmond played with passion to beat Kaikorai at Bishopscourt.
The forwards treasured the ball and were efficient with the pick and go as they took play downfield.
Joe Latta and Tom Rowe dominated the lineout and joined with Colin Enright and Chris Bell to make some dominant thrusts down field. Latta used his strength to score the first try of the game after just five minutes.
Kaikorai fullback Tony Ensor used his speed to score a try soon after this when the ball was moved wide to bring Kaikorai back into the game.
Second five-eighth Lachie Moore, the best Zingari back, used his power on a 35m run to score Zingari's second try after 26 minutes, and Willie Ripia stretched Zingari's lead to 15-11 with a penalty goal just before halftime.
Zingari sustained its pressure in the second half and the game was made safe with tries to Rowe and Bell. Its strong defence held Kaikorai out after that.
Winger Bryce Morgan and centre Jayden Spence always looked dangerous with the ball in hand and gave Kaikorai a chance.
Kaikorai's best forwards were lock Simon Grant and prop George Hendry.
Zingari-Richmond 27 (Lachie Moore, Chris Bell, Tom Rowe, Joe Latta tries; Willie Ripia 2 con, pen), Kaikorai 21 (Tony Ensor, Simon Grant tries; Cam Rutherford con, 3 pen). Halftime: Zingari 15-11.
University A 28
Pirates 14
University A gained maximum points from its win over Pirates at the University Oval but that was about its only satisfaction from an uninspiring game.
The students scored four tries to two but lost all urgency after they scored their bonus-point try eight minutes into the second half, and the remainder of the match meandered amid a glut of errors.
University led 20-0 after 25 minutes and seemed set to at least crack the half-century but its second spell was one of its most forgettable displays of the season.
Pirates was more competitive than expected, scored two good tries of its own and made much of the play in the game.
Left winger Kieran Parker scored two tries for the students and showed a sharp turn of pace, and halfback Nick Annear tried desperately to inject some life into both forwards and backs.
No 8 Sione Teu was good in patches, as was prop Tama Tuirirangi, but University will need to produce much more clinical performances as it heads towards the semifinals.
Centre Marshall Suckling, back from a long injury layoff, brought organisation to the Pirates backs and scored a good try midway through the second spell. Ben West was a lively halfback and Craig Sneddon a tidy first five-eighth.
Captain Solomon T-Pole was a hard-running, hard-working No 8, the front row held up well and Hisa Sisagi had a solid all-round game at tighthead prop, which included a determined try when he barged through the defence from close range.
University A 28 (Kieran Parker 2, Josh Dickson, Matt Faddes tries; Stephen Fenemor con, 2 pen); Pirates 14 ( Hisa Sisagi, Marshall Suckling tries; Craig Sneddon 2 con). Halftime: University A 23-7.
Dunedin 62
Green Island 23
This game was over as a contest after 30 minutes when Dunedin raced to a 35-point lead into a strong breeze.
Dunedin loose forwards Hugh Blake and Gareth Evans broke the line at will, and the Dunedin backs capitalised with relish.
Greg Dyer helped himself to a brace, with the second being a magnificent solo effort from 55m as he beat at least six defenders with a series of dummies and sidesteps.
The Sharks took their foot off the throttle for the next 50 minutes with a mediocre display, which allowed Green Island to dominate for long periods. Green Island scored three tries in the process to put some respectability into the scoreboard.
Dunedin occasionally awoke from its lethargy to keep the scoreboard ticking in the second half. Evans helped himself to three tries as he brushed off some inept tackling with contemptuous ease.
Dyer and Trent Renata were the best Dunedin backs, and Liam Ward and Sione Pulu were strong out wide.
Evans and Blake were strong ball-runners, Mark Grieve-Dunn was a tower of strength in the middle row, and Richard Thompson, in his 100th game for the Sharks, was a constant source of lineout possession.
For Green Island, Terry Gough was industrious up front, and Tala Fagasoaia and Fapene Popoali'i were the pick of the backs, although the latter should give more thought to his passing game.
Dunedin 62 (Gareth Evans 3, Greg Dyer 2, Sione Pulu 2, Liam Ward, Mark Grieve-Dunn, Will Henry tries; Dyer 6 con), Green Island 23 (Terry Gough, Simon Tupu, Tala Fagasoaia tries; Shane McNoe con, 2 pen). Halftime: Dunedin 38-13.
