North Petherton Seconds turned over too much ball in a poor display at home on Saturday. The visitors made the better start and scored the opening try.
On 20 minutes, Petherton were unlucky when flanker Chris Mantyk charged down a kick and dived on the ball over the line. But the referee said he had been unsighted and Wivy went straight to the other end for a converted try, which put them 12-0 up.
With the advantage of the slope and the low, dazzling sun at their backs in the second half, the home side piled on the pressure. Centre Chris Wand and winger Paul Hill scored tries wide out which cut the deficit to 12-10, but Wivy sealed victory with their third try near the end.
Mantyk, who is joining the RAF in the spring, was outstanding for Pethy, while veterans Mark Sutherland-Earl and Mark Innalls impressed also.