Wellington weren't helped by a couple of missed penalties of their own before they finally got on the board. The hill they had to climb got even larger when a soft defensive effort saw Tasman winger Will Jordan scoot through the line for the game's opening try in the 15th minute. Fullback David Havili found his way across the chalk just eight minutes later, after Mitch Hunt eased through some poor tackling to send his fullback in untouched.
Wellington got over the stripe late in the half through Alex Fidow, but had everything to do facing a 23-14 deficit at the break.
Credit where credit is due, Wellington came out fighting with the heart of a lion. While Tasman posted the first points of the half with another Hunt penalty, Wellington put themselves in position to make a real contest of the match.
With most of the half played in Tasman territory, Wellington worked hard to find their way across the line to at least make Tasman start to feel some sort of scoreboard pressure, but Tasman's defence was impenetrable.
A number of times Wellington had the ball within 10m of the try line, but could not force their way through Tasman's wall. Other times the Lions looked to threaten before being stymied by handling errors and poor passing.
With time almost up, one of those handling errors led to a Tasman counterattack, which saw Jordan score his second try of the game and put the final touch on their season of domination and become the first team since Auckland in 2007 to finish the season unbeaten.
The Mitre 10 Cup is joining the Farah Palmer Cup in the South Island, after Canterbury's third straight title win.
The defending champions claimed a 30-20 win over Auckland, pulling away from their northern rivals in the final 20 minutes of the game thanks to a try from midfielder Lucy Anderson, which was converted by Kendra Cocksedge. Cocksedge sealed the win in the final minutes, slotting a dropped goal to put the result beyond doubt.
Tasman 31 (Will Jordan 2, David Havili tries; Mitch Hunt 2 cons, 4 pens)
Wellington 14 (Alex Fidow try; Jackson Garden-Bachop 3 pens)
HT: 23-14
Tasman v Wellington - as it happened