"That is one of the biggest number of entries we have had. It is up there with the national [champs]," he said.
He said the New Zealand Downhill series was a five-round event, and marked the first big downhill event of the season.
Hamilton said Walker had two great runs on Saturday to win the pro elite category.
"What makes it even more remarkable is he was on a borrowed bike," he said.
Hamilton said the track was in great nick on Saturday after plenty of dry weather in the lead-up. He said there were no serious injuries on the day.
The riders had practice sessions in the morning on Saturday before getting two timed runs in the afternoon. Your fastest timed run went towards your overall placing.
The second fastest rider on the day was Nathan Rankin (3m 29.05s) followed by young star Keegan Wright (3m 29.67s).
The James Dodds Memorial Trophy was created in memory of the late mountain bike enthusiast.
Hamilton said Dodds was well known in Rotorua as a track builder and bike manufacturer and was really involved with the Rotorua Mountain Bike Club.
Dodds also helped out with junior riders at Descend Rotorua. It is the second year in a row Walker, from Kawerau, has won the Memorial Trophy.
The next four events for the New Zealand Downhill series will be held in Wellington (October 11), Napier (November 1), Taupo (November 22) and Auckland (December 13).
New Zealand Downhill series winners in Rotorua (round one):
Pro elite: Matt Walker
Open men: Des Curry
Open women: Sarah Atkins
Masters men (40-plus): Stephen Humphries
Masters men (30-plus): Leon Duggan
Under-19 men: Connor Hamilton
Under-17 men: Cole Lucas
Under-15 men: Charlie Makea
