He won the national MX1 title for the first time in 2011 and then won it five consecutive years from 2013 to 2017, but he admits he's a "little bit behind" in his preparations for the nationals this year.
"We found out a few good things with the bike at Woodville and I've got a few more things to test and try this week."
Cooper has his focus on winning the national championships again and was "feeling great physically".
"The track was very demanding, but I managed to flow well with it. I think my ability to get good starts made a huge difference. Auckland's Hamish Harwood did well to win the final race from me. Good on him."
Meanwhile, Hamilton's Chris Power took a Honda CRF450 to win the novelty River Race at Woodville on Sunday.
Power convincingly won both the day's races and he finished the day eight points clear of his nearest challenger, Palmerston North's James Galpin, the young man who had won the River Race at Woodville in 2016.
After round one of the New Zealand Motocross Championships in New Plymouth this Sunday, the series heads to Rotorua for round two on February 25. Round three is set for Hawke's Bay on March 11, with the fourth and final round in Taupo on March 24.