From outside of the top 10 at the end of lap one, Knight chipped away at the riders ahead of him, on his Honda CRF450X, and slotted himself into second place at the start of his final lap.
"It would have been nice to be able to challenge Liam [Draper], but he was long gone by the time I got through the traffic," he said.
Knight held on until the finish and the runner-up result was enough to wrap up the series win overall. May finished fourth on Saturday and ended the series second overall, 10 points adrift of Knight.
Wilkins, Grey and Reardon rounded out the series top five.
"This is the first time I've done a full Dirt Guide Series campaign," Knight said.
"It was my first time on this bike and I loved it. The Honda CRF450X has a six-speed gear-box and is a little more mellow than the motocross version.
"It has a bigger fuel tank, great for cross-country races, and a speedo on it too. I looked down at the speedo when I was racing along one of the gravel roads and I was going 115km/h ... that would be pretty scary but I wasn't thinking about that. I was just concentrating on racing."
Taupō's Wil Yeoman won the earlier 90-minute junior race and secured the overall Junior Grade (12-15 years) trophy. Whakatāne's Hayden Power won the Intermediate Grade, Waipahihi's Lisa Flanagan was best of the Novice Grade riders and Masterton's Max Williams topped the Mini Grade overall.
In terms of class wins, Yeoman won the 12-15 years' up-to-200cc two-stroke class, Eketahuna's Luke Brown won the 12-15 years' 250cc four-stroke class, Kumeu's Josh Wyatt won the 12-15 years' 85cc two-stroke and 150cc four-stroke class, Williams won the 7-11 years' Mini MX bike class and Taupō's Sam Brear took his Honda CRF80 to win the 7-11 years' Mini trail bike class.