Buist drove his Mitsubishi Lancer Evo 6 home first by 1min 3sec over Gore driver Paul Cross, who delivered a standout performance in his first full rally in his Mitsubishi Lancer Evo 4.
In taking second place in his home event, he also clinched the 2008 Southern Rally Series.
Cross said he was rapt with the outcome in what he described as his rally career highlight.
He and co-driver Wade Horrell recorded the second fastest time in the first stage and maintained a constant presence in the top four in every subsequent stage.
Gore's Andrew Graves managed a sixth overall in his Mitsubishi Evo 3 - after puncturing - which gave him second place in the southern series, followed by Clinton's Derek Ayson.
Ayson was 10th overall, the top two-wheel drive car home and can claim a top 10 finish for his home rally in each of the nine years he has entered. Nelson driver Greg Teece was third overall in an Evo 6.5RS, his result elevating him to win the South Island four-wheel drive Rally Xtreme qualifying series.
Buist took the lead on the second stage after Teece held it briefly after winning the Pukerau Forest opening stage.
Buist said he had no problems and concentrated on just keeping it on the road.
Of the 75 who started the nine muddy, predominantly forestry special stages, only 50 finished.
The victory extends Buist's points lead in the Mainland Rally Series and also sees him qualify for the finals of the Rally Xtreme Series.
The top Otago finishers were Steve Wellington (14th overall), with his brother, Mike Wellington, one place behind.
Top seed Kieran Hall, of Nelson, was second in stage 5 when an electrical problem shut the engine down.
The retirement has ended his Mainland Rally Series hopes although he has qualified for the Rally Xtreme finals.
Other top retirements were Christchurch's Jeff Judd who withdrew as planned and John Giltrap, of Lincoln, who crashed out in stage 5.
The South Island Rally Xtreme 4-wheel drive leader coming into the event, Paul Nicoll, of Nelson, had withdrawn before the start.
Buist won the Rally Xtreme section of the event, while Christchurch's Marcus Van Klink sealed the 2-wheel-drive section.
Gore Rally photo slideshow at: www.drivesouth.co.nz
