From a five-metre scrum, Waikato swung the ball out wide.
Mathis, usually a flanker, used his footwork to step through the defence and score.
Cruden was unsuccessful with the conversion and Waikato led 12-0 after 16 minutes.
There was no change to the score at halftime, with the Mooloo men in front.
Waikato again extended their advantage to 15 points with a successful drop goal from fullback Tepaea Cook-Savage.
After a poor clearance from the home team, the ball fell for Cruden, who passed the ball back to Cook-Savage.
He lined up a successful drop goal from 45 metres out.
However, Taranaki finally got on the board at the 53rd minute mark when halfback Adam Lennox crossed the chalk.
Then at the midway point of the second half, hooker Bradley Slater also scored.
Stephen Perofeta converted both tries to make it a one-point game with 20 minutes to play.
In the end, Waikato held out the home team, while maintaining their slim margin to book a Bunnings NPC semifinal against the Lions in Wellington this weekend.
Taranaki 14 (Adam Lennox, Bradley Slater tries; Stephen Perofeta 2 conversions)
Waikato 15 (Ollie Norris, Oli Mathis tries; Aaron Cruden 1 conversion, Tepaea Cook-Savage 1 drop goal)
HT: 0-12