McMillan and co-driver Murray Wright prevailed in their Subaru Impreza WRX Sti by just 6.3sec from Carter Strang/Catriona Flynn (Wallacetown, Mitsubishi Lancer Evo 10) and brothers James and Harry Worker (Mossburn, Evo).
The Invercargill pair won the opening two stages of the MLT-sponsored rally, building a margin of 19.2sec over Strang.
Top seed Caleb Macdonald (Queenstown, Evo 6) won the third stage with Strang second and McMillan third.
McMillan and Strang shared the fastest time on the fourth stage, while Macdonald’s challenge ended as he lost a lot of time when a tyre came off the bead in the stage.
Strang won the final stage but McMillan was left with the 6.3sec advantage and the Barry Robinson Memorial Trophy.
"It was good to have a bit of luck", McMillan said.
"The car was good all day. I wanted to push in the first two stages and I was really happy to be up but I was a bit worried after stage 3 when Caleb cut the lead.
"After he went out, Carter must have made a massive push on the last stage as we were pushing hard ourselves."
James Worker was third, 1min 48.3sec behind Strang, and Deane Buist (Christchurch) was fourth in his 2WD Toyota Trueno.
Buist was well within the top 10 on every stage and claimed victory in class C.
Jeremy McIlwrick (Winton) was fifth, and with the first three placegetters not eligible for class honours, he won class D for 4WD vehicles.
Gareth O’Hara (Oamaru, Toyota Corolla) was sixth, claiming the Glen Shirlaw Memorial Trophy for the first Otago Sports Car Club driver home.
New Zealand Rally Championship leader Robbie Stokes, competing in a leased Subaru Impreza H6, was seventh and the class H winner.
Stephen Gill (Winton) was eighth in his Ford Escort FJ20, winning class G; David Clearwater (Christchurch, Evo 4) was ninth; and Shane McKenzie (Rangiora) completed the top 10 and claimed the class E spoils.
Other winners were Jake Thomas (Mosgiel, Toyota Corolla AE86, class F), Ian Warren (Dunedin, Nissan Pulsar VZE, class B) and Pat Norris (Nelson, Toyota Yaris, class A).
Queenstown driver Tom Milliken won the Barry Robinson Memorial Challenge Trophy for the first Central Otago Motorsport Club member home.
Fourth seed Derek Ayson was out early with diff problems in his leased Ford Fiesta AP4, while other retirements included Phil Terry (gearbox), Bradley Ruddenklau (mechanical) and Richard Ford (gearbox).
