A mid-race collision between Australia’s defending champion Will Power and teammate Juan Pablo Montoya allowed New Zealand’s Scott Dixon to snatch a fourth IndyCar championship crown.

Colombian Montoya, the championship leader, was on course to claim the 2015 title at the season-ending Grand Prix of Sonoma in California when he collided with Power midway through the 85-lap race.

That incident forced both Penske drivers back into the field, and Dixon took full advantage.

The Chip Ganassi Racing driver claimed the race win and won the title on a countback from Montoya after both finished on 556 points in the championship standings.

Power, who began the race from pole and was still an outside chance of retaining the series title, was devastated for Montoya.

The Australian finished seventh and said various yellow and green flags had bunched the field and had turned the race into a lottery.

“I feel horrible for Juan,” Power said. “We were all in good shape.

“But we’ve got to decide whether we’re a sport or a casino. The championship shouldn’t be decided by race control.”

Brisbane-born Dixon, the 2003, 2008 and 2013 champion, had started the day 47 points adrift of Montoya.

With Sunday’s race worth double points, Dixon was a chance of landing the title but only if Montoya suffered a misfortune like he did.

“I still can’t believe it, it was such a long shot,” Dixon said.

“You never know until the last lap. That’s what it came down to.

“We had to do our best job and that’s what we did today and luckily enough it worked out.”

Missing out on the title was a bitter pill to swallow for Montoya.

The Colombian had led the standings all season and needed just to finish in the top five to seal his first IndyCar crown.

He preferred not to dwell on his mid-race collision with Power however.

“It doesn’t matter what happened,” Montoya said.

“We fought all year. It’s just a shame. We just threw it away. We had a competitive car today to do what we needed to do but just couldn’t close it out.

“We had one bad race where it’s double points and we’re out of the championship.”

The thrilling finish was in stark contrast to the start of the race where a solemn memorial was held for Justin Wilson.

The Englishman died on Monday from injuries sustained during the penultimate race of the year at Pocono Raceway in Pennsylvania a day earlier.

The entire field of drivers linked arms in pitlane before the race to pay tribute to Wilson while the British national anthem was played.