Showing strong resolve, Wai-Coa-Bay scored in the corner through Isaac Robinson, but Canterbury hit back with some good handling providing a try to Ken Tofilau, before Sepuloni added the extras to make it 24-4.
Not to be outdone, the Stallions added an unconverted try to John Koko, via a darting run and a dummy that took him through the line to score just before the break.
The second-half saw the Bulls run in a second try to Sepuloni, before talented teen Cyrus Timo Latu added his name to the score sheet, while Sepuloni kept the points ticking over with his sixth straight conversion.
He couldn't quite convert the seventh try which was scored by Manu Weepu in the 64th minute but had a game which earned the praise of his coach, Darrell Coad.
"Sepuloni has done a lot of work off the field and outside of normal practice hours and it shows today," the first time Canterbury coach said.
"We started well, but dropped intensity near the end of the first half, but all-in-all I'm really happy with the completion rate and so happy for the boys and for me too. League is in my blood and I'm so happy with the win."
Canterbury Bulls 40 (Sauni, Sepuloni 2, Havea, Tofilau, Latu, Weepu tries; Sepuloni 6 goals)
Wai-Coa-Bay Stallions 8 (Robinson, Koko tries)