Taranaki broke an early deadlock to hit the front through Seta Tamanivalu, with the returning All Black making the most of a strong run and offload from Sean Wainui. That try helped them take a seven-point lead to the break but Banks then began steadily chipping away, gradually atoning for the loopy pass he threw that was intercepted by Beaudein Waaka for the visitors' second try.
Fonotia struck 20 minutes from time and Banks added the extras to pull Tasman within one, as the errors began to pile up in the Taranaki attack and prevent them from edging further in front.
And, after Banks put them in front for the first time since the opening minutes, Tasman were left to breath a sigh of relief when the TMO denied Sione Lea a late try after correctly spotting offside in the build-up.
The win was Tasman's second from three games and allowed them to pull within three points of current leaders Counties-Manukau.
Tasman 25 (K. Fonotia try; M. Banks 6 pens, con)
Taranaki 20 (S. Tamanivalu, B. Waaka tries; M. McKenzie 2 pens, 2 cons)
Halftime: 6-13