"It's incredible. I'm as happy as can be," said Guay, putting his win down to "forgetting about everything and having a fun race."
It was a banner day for Canada after Norway seemed sure to also take bronze in an event it dominates. But late-starting Manny Osborne-Paradis edged World Cup champion Aleksander Aamodt Kilde off the podium.
On his 33rd birthday, Osborne-Paradis claimed his first career championship medal, trailing Guay by 0.51. He was serenaded by a finish-area crowd, and later was hugged by his mother.
Guay added super-G gold to his downhill title from the 2011 worlds in Garmisch-Partenkirchen. It was at the same German course last month that he wiped out in a twisting fall.
"I was lucky to walk away with fairly minor injuries," said Guay, competing at his seventh worlds. "I can see (the crash) on TV no problem, but in my head I can't really remember going off the jump and having that fear."
There were more jumps to handle Wednesday on a hill that launched racers airborne, testing their balance and ability to improvise through an unfamiliar gate-setting.
Among several racers who crashed, Tommy Biesemeyer of the United States trailed Guay by just 0.30 at midway when sliding out. Biesemeyer dislocated his left shoulder and was in a stable condition, race organizers said.
The most serious injury was suffered by Olivier Jenot of Monaco. He was airlifted by helicopter and treated in a hospital at nearby Chur for lung bruising and internal bleeding. Jenot's condition was also said to be stable.
Though Norway's men won five of the past seven Olympic titles in super-G, the nation's winless streak at the worlds was extended to nine.
Jansrud and Kilde were 1-2 in the leader's box, separated by just 0.09 after Kilde's wild ride down the final slope, and celebrated by bumping fists in the finish area.
At that moment, Guay was about to start wearing bib No. 14 and raced down leading Jansrud at every time check.
"Erik today showed us how it's supposed to be done. I'm not feeling any disappointment over that," said Jansrud, the youngest of the medalists at 31.
Guay took the record for oldest world champion from Hannes Reichelt, who set it winning the super-G two years ago in Beaver Creek, Colorado. The Austrian placed 10th on Wednesday.
Though it has been seven years since Guay won a season-long World Cup title in super-G, his third-place finish in December in Val Gardena, Italy, hinted at his potential.
Osborne-Paradis has not finished on a World Cup downhill podium in almost two years, and not since November 2009 in super-G. He began this season wearing bib numbers in the 50s as an unconsidered longshot.
Wearing No. 26, still outside the top-ranked group, he was inspired by his long-time friend.
"I got pretty fired up because of Erik," said Osborne-Paradis, who returned to form three months after becoming a father. "It was more intense having a kid, I can tell you. You can't unsee those things."
Switzerland's best result on Wednesday was eighth-place Carlo Janka, trailing Guay by 0.99. Its main pre-race hope, Beat Feuz, was 12th, and now has Jansrud and the revived Canadians carrying momentum into Saturday's marquee downhill.