"I just wanted to win because I won it last year as well.
"When I turned the wrong way, [the runnerup] passed me."
Lambert got the lead back and completed the run in just over 30 minutes.
Schoolmate Zach Bellamy, entering the fun run for the first time, took out the 5km race, which starts on the same route as the 10km race but turns around at the Waimarie berth on Taupo Quay.
"Me and George wanted to win both races. It's good," Bellamy said.
He had been coming third until the final bridge crossing, and had to put on the gas to win it from there.
Bellamy will now consider doing the 10km race next year to see if he can challenge Lambert.
Veteran walker Pete Monrad took out the 10km walk in a repeat of 2017.