Openside flanker Will Tremain squeezed through the desperate defence to score, making it 12-0 at the break.
The Maroons fired back after the break with number eight Iakopo Mapu breaking countless tackles on his way to two tries in 15 minutes after play resumed.
Lock Andrew Gardner gave them the lead with a try on the hour mark and Taradale opened the game right up with some expansive play.
Blindside flanker Josh Eden-Whaitiri scored to make it 12-22, but Marist would respond.
Tremain got his second try after a quick tap penalty close to the line, setting up an exciting finish over the last 10 minutes.
Both teams had the ball in position to score but neither could and Taradale advanced to their third straight final.
Top seed Napier Tech also triumphed in a close encounter at Whitmore Park, beating a fast-finishing Havelock North team 29-22.
First five-eighths Tamati Samuels scored the first of his two tries in the third minute with Tech thriving off a big advantage at scrum time.
A pretty set play put centre Ted Walters in for a try that made it 14-0 after 16 minutes.
Tech players Nik Patumaka and Makaro Joel had a sickening clash of heads when trying to tackle the same opposition player.
Hooker Joel recovered enough to play on, but number eight Patumaka remained prone on the field for a significant amount of time after play was stopped.
Eventually the game was restarted on a neighbouring pitch and perhaps emotions were running high because an altercation between Tech loosehead prop Tim Farrell and Havelock blindside flanker Tony Lamborn saw both players receive red cards.
Tech halfback and Nash Cup leading points scorer Sheridan Rangihuna slotted the resulting penalty goal to make it 17-0 in the 31st minute.
Havelock winger Wiremu Erkell got the Villagers on the board but Tamati Samuels scored again to make it 24-7 at halftime.
A penalty goal from Havelock fullback Trinity Neera reduced the deficit but Tech continued to have the upper hand and lock Damien Scott scored a try after sustained pressure.
Neera and winger Alex Philip both scored tries over the final 20 minutes as Havelock laid siege to the Tech tryline but their comeback proved too little, too late.