Hirscher, who was third in Saturday's slalom, secured his first win of the season, his third consecutive podium spot and fifth so far.
"I heard a lot of questions recently, like 'What's going on, you're only second?'" Hirscher said. "Whoa, I thought second was OK. But now I guess those questions are over. "
He finished 1.16 seconds ahead of Germany's Stefan Luitz, with American Ted Ligety climbing up from sixth to finish 1.42 behind in third place on the Stade Olympique de Bellevarde course.
"I think this is what the people want to see: good weather, good conditions, good skiing," the 23-year-old Hirscher said. "It's perfect to win a race, a first victory this season."
The 20-year-old Luitz had by far the best time of the afternoon to climb from 25th after his first run and secure the first podium of his career.
"It's hard to believe. But I had the perfect start conditions early on with the (better) light and visibility," Luitz, who is in the German army, said through a translator. "I knew there was a chance to do something. I think it will take all night for this to really sink in."
Pinturault was left just as stunned as the home fans by his error as he caught an inside ski and put his hand down with the finish line in sight, missing out on the chance of a second straight success after winning Saturday's slalom.
Pinturault had been second after the first run — just 0.05 behind Hirscher — but finished 28th after being a massive 2.71 seconds ahead of Luitz on the first time split.
He was perhaps trying too hard to put pressure on Hirscher ahead of his final run.
"It's a shame to come so close and to see everything crumble," Pinturault said. "Right up until the last gates I was still trying to win time and I made a mistake with the inside of my ski."
Ligety, meanwhile, has got his third podium of the season but missed out on a hat trick of giant slalom victories after winning the last two races.
"Val d'Isere's always tough, it's not a hill I particularly like," Ligety said. "It's not very user friendly, it's very steep the whole way."
Ligety was unhappy with his first run, where he finished sixth, but found some satisfaction with his second.
"I'm happy to salvage it," he said. "I'm happy to walk away from this hill with a podium when it could easily have been a DNF (did not finish)."
Aksel Lund Svindal of Norway, who finished sixth, leads the overall standings with 440 points, while Ligety is in second place with 402 and Hirscher is third on 380.
Last week, Ligety narrowly edged out Hirscher to win at Beaver Creek, Colorado, thanks to a faultless second run, but he lost time on the bottom section on Sunday and looked frustrated, lowering his head as he crossed the line.
"It's a very unforgiving hill," he said. "(Whereas) on a normal course you would have a little bobble and on this hill it becomes a big, big mistake."
Still, Ligety praised Luitz's performance.
"To be 25th after the first run and beat everyone by pretty much a second is very impressive," he said.
Ligety will skip the downhill in Val Gardena, Italy on Saturday to concentrate on slalom training. He will race Friday's Super-G in Val Gardena, and then look for more giant slalom success in the Italian resort of Alta Badia on Sunday.
Ligety leads the overall GS standings by 20 points from Hirscher.
U.S. men's coach Sasha Rearick said it was a disappointing day overall, with Tommy Ford and Robby Kelley failing to qualify for the second run. Will Gregorak did not start the first run.
"We as a team skied too conservative in the first run," Rearick said. "Fortunately, Ted is such a fast skier that skiing conservative still keeps him in the game."