A 10-0 halftime lead eventually eased out to a comfortable margin thanks to another fine performance from fullback Jordan Trainor, with the 20-year-old set to be in serious consideration for a spot in the full-strength Waikato backline.
Capable of playing on the wing as well, the New Zealand youth international crossed twice for the hosts to halt any thoughts of a stunning upset.
Wanganui made their mark on the encounter though with some well-deserved second-half tries, including an intercept effort by Gavin Thornbury which aided the visitors to their best Shield performance since 1977.
The game also marked the first start in 11 years for Waikato halfback Isaac Boss, who has returned to the province for whom he debuted a remarkable 17 years ago.
Waikato visit Tasman in their season opener before putting the Shield on the line against North Harbour in their first defence of the 2016 campaign.
Waikato 32 (Trainor (2), Tavuyara, Taufui, Douglas, Misa tries, Trainor con)
Wanganui 12 (Thornbury, Hughes tries, Whale 2 cons)
Halftime: 10-0