The second race ended with a surprise victory for Frenchman Gautier Paulin (450cc), a title contender in MX2 this year, over Italy's Davide Philippaerts (450cc) and the USA's Ivan Tedesco (450cc) - all covered by less than four seconds.
A 30 second gap then followed to Musquin (top 250), as France leaped to the head of the standings by a healthy 12 points - although with the worst moto result to be dropped at the end of the day the leaderboard was sure to change considerably after race three.
A lowly 25th for Weimer saw the USA slip to third behind the consistent Belgium, seventh and eleventh in race two with Steve Ramon (450cc) and Joel Roelents (250cc), while Great Britain dropped 23 points from the lead in fourth.
But the biggest race two losers were Italy, with Guarneri retiring after a clash with Australian Michael Byrne on lap two, dropping the home team to sixth - and in need of two strong finishes from star riders Cairoli and Philippaerts in the final moto.
Nations top ten after Race 2:
1. France - 25
2. Belgium - 37
3. USA - 39
4. Great Britain - 48
5. Republic of South Africa - 54
6. Italy - 56
7. Germany - 60
8. Australia - 66
9. Estonia - 85
10. New Zealand - 85
Race 3 (MX1 & OPEN):
The final moto opened with a massive tangle on the start straight, which left race one winner Cairoli down and out with a broken bike - and ended Italy's hopes.
“It was a pretty big crash,” said Toni. “I was full gas along the straight and I think it was Paulin who closed my line a bit from the inside and then someone else squashed me from the outside, once we touched then we went flying.”
Paulin and Byrne were also out on lap one, while Reed was left to fight his way forwards after also falling.
Up front, Jonathan Barragan led the early laps, before being overtaken by Dungey. The young American, making his first competitive foray on an MX1 motorcycle, then rode to an eleven second victory ahead of Ramon (Belgium), Philippaerts (ITA), Barragan (SPA), Frossard (FRA) and Coppins (NZL).
But seventh place for Dungey's team-mate Tedesco, who had been just 13th on lap one, was enough to hand Team USA overall victory by eight points over France, once Weimer's worst result had been removed.
Scrubbing Paulin's DNF allowed the French team to claim second over Belgium, but Italy were hit hard by the double DNFs of Guarneri (race two) and Cairoli (race three). With only one of those dropped, the team sank to sixth in the final standings.
The individual class honours went to Dungey (MX1), Musquin (MX2) and Philippaerts (Open) - and Dungey's 3-1 race results made him the hero of Team USA on Sunday. Tedesco recorded 3-7 finishes and Weimer 8-25 (the worst of which was dropped).