The former downhill World Champion was the last rider down the hill after a solid qualifying round on Friday.
He charged to the top of the leaderboard early in his run and never looked back as he surged ahead of title hopeful, Aussie Mick Hannah and hometown rider Greg Minnaar.
Hannah had suffered a 'mechanical' during Friday's qualifying and so started some way down the list in the finals. He bettered the previous best time of the day set by South Africa's Andrew Neethling by more than eight seconds to power into the 'Hot Seat'.
With just Minnaar, Josh Bryceland of England and Gwin left to start their runs, Hannah's nerves were clear for all to see as he looked to go one better than the result he achieved at the same course at the 2013 World Champs.
Minnaar, however, appeared to have the better of his Australian rival in the first two sectors. A slow final sector by the defending World Champ and a top section mishap by Bryceland allowed Hannah to maintain his position.
Minnaar, who won the 2012 World Cup and 2013 World Champs, put in a top performance since he tore his anterior cruciate ligament in the final leg of the World Cup series in Austria late last year, and was satisfied with the outcome.
"I was really nervous up top, I wasn't super comfortable riding all the technical stuff," said Minnaar.
"I haven't had a lot of time on my bike since my surgery so I just tried to suss things out beforehand.
"I had a really good run up top and I survived but, given the condition I'm in and a lack of time on the bike, I'm still really happy with my third place." Frenchman Loic Bruni crossed the line in fourth with Troy Brosnan of Australia fifth.
In the women's downhill, Manon Carpenter of Britain powered her way to her first ever World Cup win ahead of fellow Brit and current World Champion, Rachel Atherton.
"I couldn't have asked for a better start to the season because I was really stressed coming into this race," said Carpenter.
"So I am just really glad that I managed to pull it off today. I was feeling good after practice yesterday.