Marco Andretti gambled on fuel Sunday and became the youngest winner of a major U.S. open-wheel event, beating Dario Franchitti by 0.66 seconds to take the Indy Grand Prix of Sonoma.

While most of the field pitted on lap 51 of the 80-lap IndyCar Series race, Andretti stayed out to take the lead, then stretched his fuel for the final 30 laps to take the checkered flag in the next-to-last race of the season.

The 19-year-old Andretti said it was a bigger thrill than finishing second this year in the Indianapolis 500. The previous youngest winner in a U.S. open-wheel race was Scott Dixon at 20.

"This was a win," he said. "The guys were just brilliant in the pits."

Andretti won in front of his father, Michael, co-owner of Andretti Green Racing, and his grandfather, Mario, the 1978 Formula One champion.

Michael Andretti told his son to conserve fuel in the final 10 laps, even when Franchitti got around Tony Kanaan and began closing in.

"I knew he was coming," Andretti said. "It was the toughest thing I had to do _ go fast and try to save fuel."

Vitor Meira finished third, 10.65 seconds behind the winner, followed by Dixon and Helio Castroneves.

Castroneves' finish edged him into the IndyCar points lead by one over his Marlboro Team Penske teammate, Sam Hornish. Hornish, who entered the race with a seven-point lead over Castroneves, finished ninth. Target Chip Ganassi teammates Dan Wheldon and Dixon are 19 and 21 points, respectively, behind Castroneves.

"It's really close. We came here to take as many points as we could," Castroneves said. "Now, let's go to Chicago. The odds are it probably will help Sam a little because he's more familiar with the ovals. I can't wait. I wish the race could be next week."

The event at Infineon Raceway's 12-turn, 3.64-kilomter (2.26-mile) road course eliminated Meira and Kanaan from championship contention, setting up a two-team shootout at the final race September 9.

Franchitti, who could not gain ground on Andretti after a final yellow with seven laps to go, praised the rookie.

"He was definitely a little bit faster than I was today. He drove a great race," Franchitti said. "That last yellow probably cost us the win because Marco was having fuel problems."

It was Franchitti's best finish of the season after finishing third in Richmond.

Andretti, who fought a chest cold this weekend, started the race second, next to pole sitter Dixon. Dixon ran away from the field until problems with a tire change on lap 51 dropped him out of contention.

The winner, who turned 19 in March, sipped sparkling cider in victory circle. He also won here a year ago in an Indy Pro Series race.

"Marco drove like a true champion today," his grandfather said.