Mettam is no stranger to winning titles, having collected the Suzuki Series' 600cc Formula Two trophy in 2015 and the national 600cc supersport title in 2016, but he was up against Moir at the height of his powers.
And when Moir battled his way to a runner-up finish in the day's second F1 race at Whanganui, passing the chequered flag just 2.6 seconds behind another Suzuki GSX-R1000 rider, Lower Hutt's Jay Lawrence, the Suzuki Series crown was all his.
Mettam finished fourth in that second F1 race and he secured the F1 class No 2 spot for 2017, with Whakatane's Mitch Rees (Honda CBR1000) claiming the third podium position for the series thanks to his pair of sixth places at Whanganui.
All that remained to make it a perfect weekend for Moir would be for him to win the stand-alone multi-class champion-of-champions Robert Holden Memorial feature race and that is what he proceeded to do, crossing the finish line 1.5 seconds ahead of Lawrence, with 600cc Formula Two class winner Shane Richardson (Kawasaki ZX6R), of Wainuiomata, completing the Robert Holden race podium.
Rees' father, Tony Rees, was unable to defend his Robert Holden Memorial feature race trophy after crashing out of the Suzuki Series at round two at Manfeild two weeks earlier.
"I've never won the overall here at the Cemetery Circuit before, but to do that, win the Suzuki Series and take the Robert Holden trophy as well ... it's just fantastic feeling. I don't think it's sunk in yet," said Moir afterwards.
"I've won one race here in the past and finished runner-up a few times, but never this. I even managed to set my personal best Cemetery Circuit lap time in the Robert Holden race."
Richardson was also impressive, winning the 600cc F2 class with a race to spare and then powering through traffic to finish third overall in the all-capacities Robert Holden feature race.
Aucklander Nathanael Diprose (Suzuki GSX-R450) was almost untouchable in the Formula Three class, beaten just once in the series' six F3 races.
Huia man Diprose qualified fastest at all three rounds and, with five wins from six starts, had wrapped up the class with a race to spare – Whanganui's Ashley Payne (Suzuki GSX-R450) winning the final race of the day at Whanganui.
Auckland's Gavin Veltmeyer (Suzuki GVR645) sealed the overall runner-up position for the series, with Payne settling for third overall in the F3 class.
Home town hero Richie Dibben (Honda CRF450) was unbeatable in the super moto class, taking his modified motocross bike to six wins from six starts, as well as gaining maximum points for qualifying fastest at all three rounds.
He finished the series 21 points ahead of arch rival Duncan Hart (Yamaha YZ450F), the Tauranga man who'd won the class last season.
Final leading standings in the 2017 Suzuki Tri-Series.
Formula one: 1. Scott Moir (Taupo, Suzuki) 137 points; 2. Daniel Mettam (Glen Eden, Suzuki) 122; 3. Mitchell Rees (Whakatane, Honda) 112.
Formula two: 1. Shane Richardson (Wainuiomata, Kawasaki) 145; 2. Toby Summers (Manukau, Kawasaki) 115; 3. Rogan Chandler (Upper Hutt, Yamaha) 115.
Formula three: 1. Nathanael Diprose (Auckland, Suzuki) 149; 2. Gavin Veltmeyer (Auckland, Suzuki) 114; 3. Ashley Payne (Whanganui, Suzuki) 108.
GIXXER Cup (after two rounds): 1. Blake Ross (Paeroa, Suzuki) 83; 2. Clark Fountain (Greymouth, Suzuki) 76; 3. Tarbon Walker (Whanganui, Suzuki) 70.
GIXXER Cup (round three points at Whanganui): 1. Zak Fuller (Taupiri, Suzuki) 44; 2. Hunter Stoneman-Boyle (Whanganui, Suzuki) 40; 3. Michael Wilson (Invercargill, Suzuki) 32.
Post Classics Pre-89 (senior, over-600cc): 1. Glen Skachill (Lower Hutt, Bimota) 153; 2. Matt Eggleton (Rotorua, Yamaha) 128; 3. S.J. Cavell (Napier, Yamaha) 116.
Post Classics Pre-89 (junior, under-600cc): 1. Dean Bentley (Lower Hutt, Yamaha) 140; 2. Tony Sklenars (Whanganui, Honda) 105; 3. Steven Gregg (Masterton, Honda) 99.
Bears (senior): 1. Dwayne Bishop (Whanganui, Aprilia) 137; 2. Steve Bridge (Ngaruawahia, Ducati) 122; 3. Eddie Kattenberg (Te Awanga, Ducati) 111.
Bears (junior): 1. Zurrin Wiki (Hamilton, Triumph) 153; 2. Glen Eggleton (Rotorua, Ducati) 107; 3. Robert Lammas (Palmerston North, Triumph) 98.
Super Motard: 1. Richard Dibben (Whanganui, Honda) 153; 2. Duncan Hart (Tauranga, Yamaha) 132; 3. Aden Brown (Whanganui, Suzuki) 108.
Sidecars (F1): 1. Barry Smith and Tracey Bryan (Tauranga, LCR) 146; 2. Adam Unsworth and Bryce Rose (Auckland, Windle Honda) 132; 3. Chris and Richard Lawrance (Auckland, LCR Suzuki) 99.
Sidecars (F2): 1. Tim Reeves and Mark Wilkes (UK, LCR Honda) 128; 2. Tony Baker and Shelly Smithies (Penrith, UK, Baker Suzuki) 107; 3. Gordie McKeown and Geoff Davies (Tauranga, Honda) 77.
Pre-82 sidecars (Whanganui only): 1. Bryan Stent and Tracey Bryan (Whanganui, BMW) 51; 2. Robert Hood and Mark Thompson (Whanganui, Norton Commando) 42; 3. Bruce Roberts and Jim Bilby (Kimbolyon, Triumph) 34.
Robert Holden Memorial Feature Race (Whanganui only): 1. Scott Moir (Taupo, Suzuki); 2. Jay Lawrence (Lower Hutt, Suzuki); 3. Shane Richardson (Wainuiomata, Kawasaki); 4. Daniel Mettam (Glen Eden, Suzuki); 5. David Hall (Te Awamutu, Suzuki).