Dunedin slipped back one place following its 24-24 draw with Kaikorai.
Harbour edged Green Island 27-20 and remains in third, while Alhambra-Union is just outside of the top four following its 38-28 win against University.
Southern: 39
Taieri: 20
Back-up Highlanders midfielder Tei Walden gave the Southern backline the direction it has been missing most of the season.
He slotted in at second five-eighth and produced a commanding performance in the convincing 39-20 win against Taieri at Peter Johnstone Park.
The 24-year-old scored the game's opening try, cutting back on the angle and running through a gap to score from close range.
He had a hand in two more tries in the second spell. He intercepted the ball to set up centre Paul Tupai for the second of his two tries, and he made a clever cross-field kick which bounced nicely for winger Rema Smith in the final act of the game.
But as influential as Walden was, the forwards still did the bulk of the work, grinding the ball up field one ruck at a time.
Highlanders loose forward James Lentjes, who had been sidelined since injuring his elbow in March, started the second half for Taieri and made a big impact with two tries.
Southern's late try aside, the Eels had the better of the final quarter of the match.
Loose forwards Kyle Harris and Harry Flood were impressive for Southern, and Josh Walden was efficient at halfback. Lock Axel Hohneck was another standout, while prop Simon Knight played his 100th game.
Lentjes was superb for Taieri and lock Vinnie O'Connell was combative.
Harbour:27
Green Island: 20
Bottom-of-the-table Green Island almost gatecrashed Harbour's 25th jubilee celebrations.
In a torrid encounter, Green Island appeared on track for the upset of the season when it scored two tries to jump out to a 12-3 lead within the first 15 minutes.
Not until a rather fortuitous intercept 10min later, by Harbour midfield back Sio Tomkinson, did the score line start to close.With no love lost in the forward exchanges, Green Island continued to have the higher numbers on the scoreboard. It extended its lead by three, with a long-range penalty goal to Shane McNoe, and headed into the break 15-10 ahead.
With Ben Whale once again leading by example, the Harbour pack started to gain some ascendancy. But it was given little quarter with a man-of-the-match performance from Green Island hooker Peter Mirrielees, who led his side with passion and commitment against his old club.
With both sides losing their first five-eighths in the first half to injury, it was the turn of the locks to experience the comforts of the sideline, as they each sat out 10min of the second half for ill-discipline.
Nevertheless it was a game Green Island could have gone a lot closer to winning had it opted to take the points on offer when awarded handy kickable penalties. But, based on Saturday's performance, it will be a side not to be taken lightly as the competition progresses.
Alhambra-Union: 38
University: 28
The defence tightened and the forwards became more assertive as Alhambra-Union came storming back in the second spell to beat University 38-28 at the North Ground.
The students controlled the first spell with its dominant pack and fleet-footed backs to score four tries and lead 25-14 at the break.
Lock Josh Dickson was aggressive with the ball and dominated the lineout with six clean takes. Tighthead prop Angus Williams exerted power in a scrum that gained a tighthead.
Pacy wing Taylor Haugh scored two tries, the inside pairing of Connor McLeod and Fletcher Smith was efficient and Josh Timu added thrust in the midfield. All the student tries came from set pieces.
The students led by 14 points when Stephen Fenemor kicked a penalty early in the second spell.
The game changed in the last 30 minutes, as Alhambra-Union scored three converted tries and 24 unanswered points to win the game.
Props Witana Petley and Tristan Fuli matched the students as the Alhambra-Union scrum held its own in the second spell.
No8 Connor van Turnhout teamed up with replacement flanker Ben Tuiomanufili to pressure the student defence as Alhambra-Union scored two pick-and-go tries.
Fullback Vilimoni Koroi scored his second try, which was the match-winner, 23 minutes into the second spell.
Halfback Caleb Gray was tidy and first five-eighth Zac Porter kicked seven goals from eight attempts, to score 18 points.
Dunedin: 24
Kaikorai: 24
This was a strange old game.
Dunedin started with a hiss and a roar and had all the early ball and territory but it threw the first of many terrible passes which Kaikorai winger Jordan McEntee latched on to and he scampered 80m for the try.
Dunedin stormed into the 22 off a big break by winger Mone Samate-Paul and opposite winger Zac Harrison Jones went over out wide.
Kaikorai worked itself back into the game and took Dunedin on at its own game. Prop Jonah Aiona was driven over from a lineout to give Kaikorai a three-point lead at the break.
All Dunedin's momentum was being undone by terrible passing and over-ambitious off-loads. The home team gave up a penalty right on the Kaikorai tryline. Halfback Josh Renton took a quick tap and the side swept down the field and Renton himself took the last pass to score under the bar and the game looked beyond Dunedin with 30 minutes to go.
But it was not done and after Harrison Jones was dragged down just short it, went back the other way and Samate-Paul scored in the other corner.
After 30 minutes, a Kaikorai clearing kick went astray. Dunedin flanker Hame Toma bumped off Highlander Dan Pryor and raced 30m to score and it was tied at 21-21.
Kaikorai looked like it had done enough when it kicked a penalty from out wide.
Dunedin, on the back of three quick penalties, got within range for an attempt 38m out with time almost up. But it had lost first five-eighth Louis Tili before the game and replacement and kicker Tim Cossens had hobbled off.
Up stepped replacement midfielder Charlie McCarten for his first goal kick in premier rugby and he calmly slotted it, to draw the game.
For Dunedin, Leroy van Dam was a rock in midfield and Harrison Jones was a danger out wide. In the forwards Toma, Don Brighouse and Mark Grieve Dunn were into everything and never took a backward step.
Renton and Ben Miller were tidy in everything they did. Pryor was all over the loose ball and, apart from getting on the wrong side of referee Stu Curran late in the piece, was the best in the forwards. Young No8 Iakapo Petelo Mapu was powerful on the burst and hard to bring down.
