"It was a godsend really. I don't think I would have made it back around," said Thomasen.
With his one lap advantage, Thomasen had been happy to settle in behind Sunday fast starters Raana Horan (Red Beach), Clim Lammers (Hikurangi) and Tony McCall (Manukau) in the opening laps.
But as Lammers was delayed by damaged suspension, McCall was slowed with a fuel pump problem and Horan was halted by broken steering, Thomasen's steady pace pushed him to the front of Sunday's standings.
"Today was mainly risk management," he said at the finish after more than 15 hours of driving. "It was about getting past the traffic quickly and safely and keeping up a good pace without hurting the car."
Thomasen said the NZ 1000 win was his biggest motorsport accomplishment.
"This is such a challenging event. There's a lot to keeping it all together."
Auckland racer James Buchanan rose from sixth place overnight with a trouble-free Sunday run in his Mitsubishi Evo powered car to secure the runner-up honours.
Off-road racing rookie Steve Rowe (Putaruru) - in just his second competitive event - drove another 1000cc Polaris to third place and McCall salvaged a fourth place finish in his BSL Terra-Chev.
Delahunty's drive to fifth place in another Polaris RZ-R 1000 was a significant achievement for the Papamoa College student.
He had overshot a junction on Saturday's opening lap and damaged the front suspension. After a pit stop for repairs he climbed from 52nd after lap one to 14th position overnight and gained fifth overall in the late stages of Sunday's race.