Sonoma, CA (My Sportsbook) - Dario Franchitti was untouchable in Sunday's Indy Grand Prix of Sonoma, as he led from start to finish at Infineon Raceway for his fourth IndyCar Series victory of the season.

Franchitti started on the pole and avoided a seven-car pileup on the opening lap. He then held off Ryan Briscoe from Team Penske after a late-race restart to win at the 2.303-mile, 12-turn Northern California road course for the first time.

"Track position was critical today," Franchitti said. "It probably wasn't the most interesting race for the fans, but I did what I had to do today."

Franchitti finished 0.25 seconds ahead of Briscoe, who recorded his seventh runner-up position this year. Briscoe also took a four-point lead over Franchitti with three races to go in the season.

"If we're going to win this championship, I'm going to have to win one of the last three [races] here," Briscoe said. "It's that close, it's tough. Scott [Dixon] had a tough weekend, which helps us a little bit. Dario had maximum points, and he's right there."

It's the 13th time in the last 14 races the points lead has changed hands.

Dixon fell 21 points behind after he finished a disappointing 14th. The defending IndyCar champion and 2007 race winner at Sonoma was involved in the first-lap melee after starting 10th on the grid. He got caught in a jam and drove into the back of Tony Kanaan, sustaining damage to the nose of his car. Dixon remained on the lead lap and worked his way back to 10th before Marco Andretti spun him out on the final lap.

"It was a tough race," said Dixon, who finished 12th last year at Sonoma. "Right at the end there, [Andretti] just got into the back of me and spun me around. He came up to me and apologized. He didn't do it on purpose. It's just one of those days."

Franchitti and Dixon lead the series with four wins each this season.

Rookie Mike Conway challenged Briscoe for the second spot in the final laps, but settled for a career-best third. Mario Moraes finished fourth, and Hideki Mutoh came in fifth.

Helio Castroneves, the defending race winner, also had a frustrating day at Sonoma. Castroneves' car got slightly airborne after he made contact with Kanaan heading into the esses portion of the track late in the race. Shortly after, his right front suspension failed, causing him to run off course into the dirt. He wound up finishing 18th and saw his championship hopes all but fade.

Castroneves, the Indianapolis 500 champion, now trails his teammate Briscoe by 126 points.

Ryan Hunter-Reay also stalled on the track at the same time as Castroneves' incident, which set up a wild five-lap shootout to the finish.