Briton Laurie Greenland had threatened to spoil the French Alps party mood with a great run to set a time that most of the leading qualifiers failed to beat.
After Troy Brosnan and Loris Vergier fell just short, world champion Loic Bruni stormed down the dusty course to bring the crowd to their feet at the finish.
Reigning World Cup champion Pierron, though, was a man possessed with his phenomenal sliding speed at the top setting up the chance of victory which he duly delivered on by an amazing 2.352 seconds.
It was Pierron's second 2019 win after Fort William with Bruni's overall lead now cut to just 110 points heading into the Val di Sole stop in Italy.
Pierron said: "It was just so good. The crowd in France was just mental all the way along. I knew I was good at the top, then I was on the edge and nearly crashed. I was sliding everywhere. That was my limit. The level this year is so high. I am going to fight for it."
Bruni explained: "Amaury was on fire all weekend. I was a little bit too conservative. Maybe I was thinking too much of the overall to win this one. The crowd was insane. It was so loud the whole way down. Amaury is a big threat now and it will be a good end of season."
In the women's race, Hannah took advantage of Rachel Atherton's injury to win from France's Marine Cabirou with El Salvador's Mariana Salazar a popular third.
Hannah, who also won the Leogang stop, revealed: "I haven't had two wins in one year before. To back it up after quali, I am proving something to myself and my team. To take the win is pretty mind blowing."
Cabirou, 22, said: "Race after race I am more confident and I am really happy. I am sad for Rachel, but it is more open for the other girls and good for the next race."
1. Amaury Pierron FRA 2:57.008
2. Loic Bruni FRA +2.352
3. Laurie Greenland GBR +3.450
4. Troy Brosnan AUS +4.137
5. Loris Vergier FRA +4.506
UCI MTB World Cup men's downhill overall standings:
1. Loic Bruni FRA 965 points
2. Amaury Pierron FRA 855
3. Troy Brosnan AUS 855
4. Loris Vergier FRA 614
5. Danny Hart GBR 602
UCI MTB World Cup women's downhill at Les Gets result:
1. Tracey Hannah AUS 3:27.600
2. Marine Cabirou FRA +0.677
3. Mariana Salazar ESA +2.171
4. Eleonora Farina ITA +6.080
5. Nina Hoffmann GER +6.457
UCI MTB World Cup women's downhill overall standings:
1. Tracey Hannah AUS 1040 points
2. Marine Cabirou FRA 840
3. Rachel Atherton GBR 730
4. Nina Hoffmann GER 695
5. Veronika Widmann ITA 514