Last month, Jonathon also raced in the National Downhill Championships at Nelson, where he placed fifth in his age group.
However, his successful streak came to an end in Wellington, when he crashed during the practice round, and fractured his arm.
Jonathon will still travel to Napier this weekend, but only to support his older brother and to keep an eye on fellow U-17 competitors movements on the points table.
The Kennett brothers' Tauraroa Area School mate Michael Lea also started the series, intending to contest all of the events.
Lea made a good start at the first two South Island events, before he crashed during the Mount Hutt round and broke his collarbone, ending his series.
The 16-year-old is placed seventh in the U-17s, which may change following the Napier event.
Competitors' best five results count towards a NZ Mountain Bike Downhill Cup title, and North and South Island Downhill Cup titles will be decided from points gathered at the three events in each island.