Drysdale, of Auckland, won his fourth national single sculls title when he beat arch rival Rob Waddell (Waikato) by 5.33sec in the fast time of 6min 47.32sec at Lake Ruataniwha.
Waddell clocked 6min 52.65sec and Peter Taylor (Southern RPC) was third in 6min 52.65sec.
The battle between the two world-class single scullers who battled for the Olympic Games spot will be continued at the New Zealand trials at Lake Karapiro next weekend.
Drysdale won selection for the Beijing Olympics last year but Waddell wants the spot for the world championships in Poznan, Poland in August.
Both have made it clear the single sculls is their preference for World Cup regattas in Munich and Lucerne, and for the Poland champs.
It means whoever misses selection may not feature at all when the team is unveiled on March 6.
Their contest has captured public interest and 3500 spectators crowded the banks of Lake Ruataniwha on Saturday.
Drysdale was disappointed with his performance at the Beijing Olympics but the win on Saturday has given him the confidence he needs to defend the world title he has won for the past three years.
"It's nice to come out first up and get a win like that," Drysdale said.
But he knows Waddell is a tough opponent.
"Rob's a good athlete and I know he'll be coming back at the trials next weekend," Drysdale said.
Drysdale was pleased with his time, which ranked as 97% of the world record of 6min 35sec.
This was notable, as Ruataniwha is not regarded as a fast course.
"Had the championships been held at Lake Karapiro it would probably have been a world record," Southern Regional Performance Centre manager John Wylie said.
Waddell's time was 95.7% percent of the world record and Taylor's 93.9 %.
The criteria for New Zealand selection is 94 % or better.
"It was one of the best races I've ever rowed," Drysdale said.
Waddell, meanwhile, is determined to remain in contention for the single sculls spot.
"There is only one spot for the world championships and there are two guys who want it. I'll be approaching next weekend with a lot of vigour," Waddell said.
"I want to go in the single. That's the spot I want to take."
Waddell realises he still has much work to do to achieve his goal.
"I've got a week to get it together before the trials. I know I can do better than that. I've just got to."
