Gwin stunned the massive crowd that crammed into the forest at the Cascades mountain bike park with a time of four full seconds faster than the 4 minute 12 time that was being tipped as a title clinching mark.
"I can't understand why I was so fast today," said an elated Gwin. "I was so calm at the start. Usually I try to shy away from people talking to me but today I felt like I needed someone to wake me up."
"Maybe that's what you need to do on a course like this - stay really calm otherwise you blow up," he said.
Most of Gwin's challengers did exactly that. Australian Michael Hannah, the fastest man in qualifying and the last man to have a shot at racing inside Gwin's blisteringly fast time, crashed heavily early on, breaking his bike stem and ending the competition in a moment of high drama.
Before him British world No 1 Gee Atherton and World champ Sam Hill failed to make a debt into a title challenge, and South African Andrew Neethling's rollicking challenge ended in a crash high up on the course.
Even hometown hero Greg Minnaar couldn't upstage Gwin, despite riding a tidal wave of hysterical support and vuvuzelas from the thousands of fans packed around the course.
"I made a couple of silly mistakes early on and was trying to catch up all the way,' said Minnaar. "I can't thank the crowd enough. Their support was unbelievable and made a huge difference to me on the day. I am sorry for the second place," he added.
For much of the men's downhill final veteran downhiller Steve Peat occupied the leaders hotseat, and looked set to provide an upset result until Gwin blitzing of the 3km Cascades layout.
Gwin, who hails from California and races with the Trek World racing team, is a relative newcomer to downhilling, after converting from BMX and Motocross racing after a succession of serious injuries.
Earlier in the day the women's title fell convincingly to British women's downhill pacesetter Tracy Moseley. The 24 year old shredded the fast hard downhill course to silence her competitors.
"This is the toughest track I have ever raced," said Moseley. "I was just hanging on for dear life, after pedalling flat out through the flat section following a great start."
Moseley heard the on-course commentator say that her split times were very close to compatriot Fionn Griffiths who was the fastest women down the hill prior to Moseley's run.
"I was done," said 32 year old Moseley. "It was so tough. The course was horrid - hard and fast - and I was finished at the end." Griffith was second, holding off a trio of French youngsters Emmeline Ragot, Sabrina Jonnier and Floriane Pugin.
Earlier in the day rising Swiss star Andri Frischkneckt posted a comprehensive victory in the junior men's cross country title decider, romping home to a one-sided two minute victory over local challenger Gert Heyns, with French teenager Cyril Grangladen a minute further back in third.
The all South African junior girls cross country race was won by the current national and African champ Ashleigh Parker-Moffatt, almost a minute and half clear of Linda van Wyk, with Simone Vosloo making up the balance of the podium places.
The final day saw around ten thousand MTB fans back onto the Cascades MTB layout in near perfect racing conditions to watch the thrilling spectacle of the downhill finals.
The event organisers have lodged a very strong bid to host the 2013 World Championships at the same venue, and are bullish about their chances of winning that bid when it is decided in the coming weeks.
SUMMARY OF RESULTS
DOWNHILL Finals
Men
1.Aaron Gwin USA 4:08.634
2.Greg Minnaar RSA 4:08.875
3.Gee Atherton GBR 4:10.555
4.Fabien Barel FRA 4:12.880
5.Steve Peat GBR 4:15.443
6.Steve Smith CAN 4:15.568
7.Mark Beaumont GBR 4:15.871
8.Samuel Hill AUS 4:16.033
9.Nick Beer SUI 4:16.599
10.Josh Bryceland 4:16.915
Women
1.Tracy Moseley GBR 4:56.166
2.Fionn Griffiths GBR +00.288
3.Emmeline Ragot FRA +01.184
4.Sabrina Jonnier FRA +02.173
5.Floriane Pugin FRA +02.268
6.Celine Gros FRA +04.248
7.Emilie Siegenthaler SUI +06.344
8.Manon Carpenter GBR +15.617
9.Mio Suemasa JPN +16.238
10.Petra Bernhard AUT +16.415
UCI MTB WORLD CUP CROSS COUNTRY Finals
Junior Men
1.Andri Frischkneckt SUI 1.10:44
2.Gert Heyns RSA +02:04
3.Cyril Grangladen FRA +03:33
4.Kyle Dorkin RSA +04:34
5.Patrick Belton RSA +05:44
6.Brendon Davids RSA +05:58
7.Arno du Toit RSA +07:51
8.Evan van der Spuy RSA +09:28
9.Dylan Hattingh RSA +10:37
10.Harry Maarsigh RSA +12:33
Junior Women
1.Ashleigh Parker-Moffatt RSA 1.15:10
2.Linda van Wyk RSA +01:21
3.Simone Vosloo RSA +05:19
4.Savnnah Vosloo RSA +07:14
5.Tayla Odendaal RSA +24:30