Battling behind him are Ōpārau's James Scott, Silverdale's Hayden Smith and Mount Maunganui's Josiah Natzke, while Matamata's Brodie Connolly and Napier's Reece Lister hold a share of fifth spot overall.
In the 125cc class, it's anybody's to claim, with Hayden Smith, Clevedon's Cobie Bourke and Tauranga's Madoc Dixon the three most likely contenders.
The second of two rounds for the Women's Cup competition will also be run at Taupō on Sunday and Motueka's Roma Edwards, Opunake's Taylar Rampton and Hamilton's Amie Roberts are the leading title contenders.
The Covid-19 pandemic has kept overseas riders away this season, but this has not diluted the competition because so many of these riders are international stars in their own right.
Harwood, Cooper, Chase, Lamont, Purvis and Natzke have each represented New Zealand at the annual Motocross of Nations, in Europe or the United States, in recent years, while Scott has also raced at Grand Prix events in Europe and Connolly has raced many times in Australia.
Even the current leader in the non-championship MX3 class, Waikato's Darryll King, has huge international credentials. He was twice a World Motocross Championship runner-up and represented New Zealand at the Motocross of Nations nine times - on one of those occasions ending on the podium.
Motorcycling New Zealand motocross commissioner Ray Broad said he was looking forward to "a grand finale at Taupō for what has been a great championship series this season".
"This year the Women's Cup also concludes at Taupō and that adds even more to the spectacle," he said.
"This popular venue is centrally located in the middle of the North Island, is a renowned all-weather track and always superbly groomed and managed by the host Taupō Motorcycle Club workers. We are thrilled to celebrate and wind up the championship here."
The New Zealand Motocross Championships are supported by Aon Insurance, Kawasaki New Zealand, Pirelli tyres and Fox apparel, with Taupō's final round additionally supported by Yamaha NZ.
Senior NZ Motocross Champs points after three of four rounds:
MX1 class:
1. West Auckland's Hamish Harwood, 192 points; 2. Mount Maunganui's Cody Cooper, 169; 3. Taupo's Wyatt Chase, 159.
MX2 class (provisional): 1. Mangakino's Maximus Purvis, 194 points; 2. Oparau's James Scott 154; 3. Silverdale's Hayden Smith, 151.
Under-19 class: 1. Matamata's Brodie Connolly, 150 points; 2. Te Aroha's Luke Van Der Lee, 145; 3. Christchurch's Marshall Phillips 128.
MX125 class: 1. Silverdale's Hayden Smith, 179 points; 2. Clevedon's Cobie Bourke, 172; 3. Tauranga's Madoc Dixon, 164.
MX3 class: 1. Matamata's Darryll King, 137 points; 2 Whakatane's Darren Capill, 122; Tauranga's Brendon White, 85.
Women's Cup (after one of two rounds): 1. Motueka's Roma Edwards, 72 points; 2. Opunake's Taylar Rampton, 69; 3. Hamilton's Amie Roberts, 58.
