The worst two weeks of his life led to his best day as Will Power banished the memories of his three near-misses to win the IndyCar championship.

Will Power admits he struggled with the spectre of past near misses before finally securing the IndyCar championship he craved in California.

A three-time runner-up, including heartbreaking crashes in the final race of the season in 2010 and 2012, Power finally landed the IndyCar title with a ninth-place finish in the 500-mile season finale on Sunday.

The 33-year-old sobbed as he crossed the finishing line at the Auto Club Fontana super-speedway, one of the locations of his final day heartbreaks in the past.

He’s the first Australian to get his hands on the Astor Cup, a trophy which bears the likeness of every American open-wheel champion since 1909.

Holding a 50-point championship lead and starting from a lowly 20th on the grid, Power overcame his pre-race nerves to methodically claw his way up the field.

The Australian briefly led the race following a late restart, but when main championship rival Helio Castroneves was given a drive-through penalty with 30 laps to go in the 250-lap race, he knew the title was in his grasp.

“That was one of the hardest races ever. Oh my god. I was crying over the line,” Power said.

“I’m so mentally exhausted now. My hands are numb from holding on to the wheel so tight.

“I want to be a lot more excited but I’m so drained right now. I can’t believe I’ve won it.”

Power said his wife Liz, who watched the race nervously alongside his mother Marge in the pits, had endured the brunt of his emotional battle in the past couple of weeks.

“The last 14 days have been the worst in my life, just mentally, just emotionally, just so bad,” he said.

“Not sleeping, stressing. I feel bad for my wife, keeping her up at night.

“You never think it can happen until it happens.”

Castroneves eventually finished in 14th, with compatriot Tony Kanaan taking out the win.

It’s the fourth time Castroneves has finished as the championship runner-up.

“Well done Will. You’re the champ man,” he said of his Penske teammate.

Power’s title win is the first major international motorsport championship win by an Australian on four wheels since Alan Jones’ Formula One world title in 1980.

“That’s 15 years of hard work,” Power said.

“I started taking it seriously in 2000 and (that’s) just 15 years of hard work.”