Starting the day one position above Wellington, Petherton had the game firmly under control at half time when they led 17-3.
Graig Goodwin and James Cox scored tries for the home side with Harry Roberts kicking two conversions and a penalty.
Wellingtons’s only points of the half – and the game – came from the boot of Mark Nichols who landed a penalty.
It was more of the same in the second halfas Roberts stretched Petherton’s lead with a penalty after an hours play while Jervis Manupenudashed any hopes of a late fightback by Wellington with another try for Petherton. Roberts added the extra points.