Two opportunist tries from centre Bailyn Sullivan have helped Waikato stymy Tasman's attempted NPC premiership threepeat at Hamilton.
The hometown Mooloos were pushed to the limit by the two-time defending champions, before emerging 23-20 winners - their first national title since 2006, the inaugural year of the competition.
In its centenary year, Waikato was able to claim the men's and women's double, after taking out the Farah Palmer Cup last month.
The eventual winners dominated the opening stages, but after the first 25 minutes, a lone penalty from first-five D'Angelo Leuila was all they had to show for their efforts.
When All Blacks Sevens speedster Regan Ware scorched the Waikato defence for Tasman's opening try, the titleholders seemed to have recovered their poise and suddenly looked the better of the two teams.
That changed in the blink of an eye, as Sullivan pounced on a loose pass inside his own half to sprint away and reclaim the advantage.
Leuila and Tasman counterpart Mitch Hunt exchanged penalties, and Waikato held a 13-10 advantage at halftime.
They seemed to have one hand on the trophy, when Sullivan struck again after the restart, racing away for his second try, as the Mako were left lamenting a miserly advantage played by referee Nick Briant.
The introduction of barnstorming midfielder Levi Aumua off the bench seemed to spark Tasman late and he laid the platform for lock Quinten Strange to score, levelling the contest at 20-20, but Fletcher Smith - subbed on for Leuila - slotted a penalty to edge Waikato ahead with less than 10 minutes left.
The hosts controlled field position for much of that time remaining, but as they tried to keep the ball in hand over the dying seconds, they conceded a penalty just metres out from the Tasman line, gifting their rivals one last chance to snatch the silverware.
With time up, another penalty saw the Mako deeper into Waikato territory, but in his 100th appearance for the province, replacement hooker Quentin MacDonald was wayward with a lineout throw and the Mooloos gleefully found touch to begin their celebrations.
Waikato 23 (Sullivan 2 tries; Leuila 2 penalties & 2 conversions, Smith penalty) Tasman 20 (Ware & Strange tries; Hunt 2 conversions & 2 penalties)
