Turnwald was satisfied simply to "ride safe" and finish third, that being enough to win the class outright by one point.
"I was on a borrowed KTM 125SX and decided to play it safe in the last race, with the track getting so rough and because the bike wasn't really set up for me," Turnwald explained.
"I didn't know what the points situation was [between me and Ben Broad], but I figured third place in that last race would be okay to still win the title."
That's exactly how it turned out.
With his solid performance at Mercer, it seems the BikesportNZ.com-supported rider is poised to push on to greater things on the full national scene.
Turnwald finished eighth overall in his senior New Zealand Motocross Championships debut earlier this year and believes he can improve on that when the 2015 national championships season kicks off in February.
"I'm hoping for a podium finish at the nationals," he said.
Meanwhile, Waiuku College rider Dean Collins clinched the 16-18 years' 125cc class with a similar display of strategic riding.
Dean Collins in action
The Yamaha hero took his 2012-model YZ125 to finish 2-1-2 at Mercer, ending the contest two points clear of Te Aroha's Aaron Manning (who finished 3-2-1 on his Husqvarna TC125).
"I was getting some amazing arm pump [painful forearms caused by lactic acid build-up]. I guess I wasn't as fit as I needed to be," said 17-year-old Collins.
"I led the last race for a while but then arm pump got the better of me and I slipped back to finish second.
"I knew that was good enough to win the day, so I wasn't too worried about Aaron getting past me."
Another impressive performance came from KTM rider Ben Hahn, from Pinehurst College on Auckland's North Shore. Hahn notched up a 1-1-2 score-card to easily edge out Stratford High School's Nick Hornby (Yamaha) and win the 16-18 years' 250cc four-stroke class.
Fellow KTM rider Josiah Natzke was, as expected, simply too slick for his rivals in the 14-15 years' 250cc four-stroke class.
Hamilton's Natzke, just back from a stint in Europe, where he managed third overall at the Czech Republic round of the European 125cc Championships and then seventh overall at the World Junior Motocross Championships in Belgium, showed why he is ranked among the top 10 junior riders in the world.
Riding for Te Kura High School, the CMR Red Bull KTM Team rider not too surprisingly won all three of his races at Mercer, each time finishing nearly a full lap ahead of eventual runner-up Jovhann Phillips (Tauranga Boys' College), who raced a Suzuki.
Other class winners were Andre Whitehead (Te Puke High School, 16-18 years' 250cc novice); Jordan Milsom (Te Puke High School, 13-16 years' 85-150cc); Max Simpson (Waiuku College, 13-15 years' 125cc novice); Riley Hare (Paeroa College, 14-15 years' 250cc novice); Jack Broughton (Te Kauwhata College, 85cc novice); Anna Lawton (Kaipara College, women's open grade).
Hauraki Plains College won the overall battle for school honours with 577 points, ahead of Waiuku College (496 points) and Hamilton Boys' High School (352 points). A total 39 college teams were entered, adding up to more than 140 individuals.
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