Scott Dixon clinched his fifth Verizon IndyCar Series title with a P2 finish in Sunday's season finale at Sonoma as early contact dashed chief championship rival Alexander Rossi's hopes of a maiden crown.

Entering the season finale leading Rossi by 29 points, Dixon managed to execute a smooth race that saw the Chip Ganassi Racing driver finish second behind race winner Ryan Hunter-Reay, who led 80 of the 85 laps at Sonoma.

Rossi had started the race fifth, three places back from Dixon, but dropped to the back of the field after light contact with Marco Andretti on the opening lap, leaving him with front wing damage and a puncture.

In a race without major incidents, Dixon was able to clinch the title with a straightforward run to P2, enjoying a 57-point buffer over Rossi in the final standings as the ex-Manor Formula 1 driver fought back to P7 at the chequered flag.

"The whole race I was thinking about things that were out of our control, cautions that were going to flip the field. None of that happened," Dixon said.

"It was a very smooth race, but mentally it was tough and draining. It's amazing to be in this situation, fifth championship. What this team has achieved, I'm a very small piece in that whole wheelhouse of what's going on at Chip Ganassi Racing. I feel very lucky to work with the people that I do." Dixon's fifth title puts him clear of Mario Andretti, Sebastien Bourdais and Dario Franchitti in the record books.

Will Power finished the race third for Penske despite trying to get the overcut on fuel, with teammate Simon Pagenaud taking fourth ahead of Marco Andretti.

Bourdais finished sixth ahead of Rossi and outgoing champion Josef Newgarden, while Patricio O'Ward impressed in his debut IndyCar race to finish ninth ahead of Ed Jones, who completed the top 10.