The track around the hill incorporates gravel road, bridges, switchback corners and single tracks.
It offered alternatives forks in the track where you could try your courage on a deep dip to pick up a few extra seconds, or take the steady way around.
Following Williams and thus officially winning the Expert section, was Rotorua's Peter Calnan, who lost his bike number after taking a tumble while chasing Williams through the trees.
"I run up a bank, I went to get back on [the track] and fell off.
"It was 'leave the number there and keep going'.
"I love the course, I've come to Wanganui for the sixth time now in 12 years, it's the hardest one around.
"This is aggressive, it's an honest race."
Wanganui's Graeme Cox won the three-lap Sport section in a time of 1 hour, 8.16min.
"It's a fantastic track, ridden here last Masters Games and this is the best track they've had."
An all-rounder, Cox was now looking forward to the men's 5km run on Thursday night, followed by the team triathlon at the weekend.
In a time of 1 hour, 21.26min, Hamilton's Marguerite Ritchie was the first woman home in the Expert section.
Combined with the afternoon downhill event, there were 61 riders taking part.