Scott Dixon is the IndyCar world champion for the third time in his illustrious career.



The Kiwi motor racing star has completed a superb comeback to claim the series title, finishing fifth in today's season-ending Fontana IndyCar 500 at the Auto Club Speedway in Fontana, California, and tucking away the $US1 million ($1.2 million) champion's cheque.



Dixon's season was stuck in second gear as he approached the midway point but three wins in eight days in July - one at Pocono and both races at the Toronto double-header - thrust him into contention.



He was still 49 points behind Brazilian Helio Castroneves heading into the Houston double-header a fortnight ago, but he emerged from those races with a first and second and a 25-point lead.



The series win comes five years after his last IndyCar triumph, which came five years after his first, in 2003.



It was all about Dixon and Castroneves heading into today's finale.



The Kiwi had a 25-point lead heading into the race and needed a top-six finish to wipe the Brazilian out of the equation.



Both Dixon and Castroneves readily accepted 10-place grid penalties after fitting new motors for this race, determined to do everything they can to avoid mechanical issues.



It meant Castroneves started in 12th and Dixon 17th, but grid position was never going to be an issue on a wide oval track over such a long distance.



Castroneves predictably made the early moves, bolting into second within the first 20 of 250 laps. Dixon chipped away in a race with ebbed and flowed, but by the midway point he'd moved into the top-three and was looking comfortable.



Castroneves' challenge effectively ended with 25 laps remaining when his wing came loose and he was forced to pit. He would finish sixth.



Dixon, who was challenging for the race lead, then had issues of his own; with 21 laps remaining he was forced into the pits after overheating.



But the title was never in serious doubt; because Castroneves had to win the race and Dixon had to finish outside the top six for the Brazilian to claim the spoils.



Australian Will Power won the race, with Ed Carpenter second and Tony Kanaan third.



Dixon has edged Castoneves for all three of his world titles.



In 2003, Dixon and Castroneves were tied entering the finale at Texas Motor Speedway but the Kiwi prevailed, and in 2008, Dixon led Castroneves by 30 points heading to Chicagoland Speedway finale and held him off for the title.



Dixon finishes the 19-race season with more wins (4) and top-fives (9) than any other driver.



A Target Chip Ganassi Racing driver - either Dixon or Dario Franchitti - has now claimed the championship in five of the past six years.



And it's the ninth year out of the past 10 that a Honda-powered car has won the overall title.



The only downer for the Kiwi - and it is a minor one in the washup - is that he missed a further $US250,000 bonus on offer for the best driver across the three long-distance races.