Pal Varhaug's bid to secure the runner-up position in the Auto GP World Series received a huge boost when the Norwegian took his third victory of the season in race one at Sonoma.
The Virtuosi UK driver produced a faultless drive after negotiating an opening lap melee to take the lead.
Adrian Quaife-Hobbs, who wrapped up the title at Curitiba last time out, had made a clean start from pole, but was taken out at Turn 2 when third qualifier Antonio Pizzonia cut the corner and smashed into the rear of his Super Nova car.
"Quaife-Hobbs was relatively slow through Turn 2, and it looked like Pizzonia didn't understand what was happening," said Varhaug. "It was a very strange accident, but I was very happy as it was really lucky for me."
Both Quaife-Hobbs and Pizzonia retired on the spot, and an earlier startline crash between Max Snegirev and Francesco Dracone contributed to a lengthy spell behind the safety car. The surviving cars pitted under caution at the opening of the pit window on lap five.
Front row starter Sergey Sirotkin had been delayed while taking avoiding action of the crash at Turn 2 and dropped to fourth, but a quick turnaround by the Euronova crew helped lift the Russian to third.
Sixth starter Daniel de Jong also gained ground in the stops and rejoined the safety car queue behind race leader Varhaug.
After the early dramas, the race settled down into a procession at the front of the field. Varhaug opened an advantage of several car lengths over de Jong, and took victory by 1.5 seconds on the series' first visit to the USA.
Varhaug now has a 20-point advantage over Sirotkin in the drivers' standings, with only 21 available in Sunday's season finale. Sirotkin was the only driver to start on hard-compound Kumho tires, but the decision failed to bring the anticipated performance advantage.
"I think we may have made a mistake by changing the fronts rather than the rears during the stops," said Sirotkin.
Last year's Formula Abarth Europe champion came under attack from Sergio Campana in the closing laps, but held on to take the final podium place. GP2 race winner Giacomo Ricci completed a comfortable run to fifth ahead of series returnee Giancarlo Serenelli. IndyCar racer Pippa Mann finished ninth in her series debut.
Results - 21 laps:
Pos Driver Team Time/Gap
1. Pal Varhaug Virtuosi UK 35m20.704s
2. Daniel de Jong Manor MP + 1.481s
3. Sergey Sirotkin Euronova + 3.062s
4. Sergio Campana Zele + 4.190s
5. Giacomo Ricci MLR 71 + 12.875s
6. Giancarlo Serenelli Ombra + 24.124s
7. Kotaro Sakurai Euronova + 31.442s
8. Antonio Spavone Euronova + 48.695s
9. Pippa Mann Campos + 1m00.705s
10. Michele la Rosa MLR71 + 1m02.979s
Giuseppe Cipriani Campos 8 laps
Max Snegirev Campos 0 laps
Adrian Quaife-Hobbs Super Nova 0 laps
Antonio Pizzonia Zele 0 laps
Francesco Dracone Virtuosi UK 0 laps