It was the worst moment of Marcos Ambrose's motor racing career.

A career that has taken him from go-karting in Tasmania to Europe, to two V8 Supercar championships and to the biggest race series in the US - NASCAR's Sprint Cup.

Instead of the Devil Racer he's now being called "The Blunder from Down Under" over there.

One of the usually sycophantic American TV commentators even suggested he'd be found out on San Francisco's Golden Gate Bridge, presumably preparing to jump.

It's galling, embarrassing, humiliating for Ambrose.

He was headed for his first victory in the Sprint Cup, the first by an Australian in NASCAR's premier class - and one of very few by a non-American.

Jimmie Johnson, winner of the past four Sprint Cups and seemingly a man with a Midas touch, wasn't going to catch the Aussie in the closing stages of the 16th round of the series at Infineon Raceway in Sonoma, California.

Johnson had resigned himself to taking second place this time. His tyres were too badly worn to challenge Ambrose.

But, with just a handful of laps to go, Brad Keselowski spun his Dodge and track officials waved yellow flags - the signal for caution, for the field to maintain its order behind an official pace car, and for no passing until racing resumes.

Ambrose flicked off his Toyota engine, to cruise a little, to conserve fuel.

He says he got an instruction over the radio from his pit to do that.

But as his car turned left and uphill he needed to fire the engine back up. Quickly.

It wouldn't crank.

Ambrose wants to believe his No 47 car didn't come to a halt, but the TV footage tells otherwise.

Seven cars went past him, led by Johnson.

When Ambrose's motor belatedly spluttered back to life he tried to regain his position, but NASCAR told him he couldn't.

He was ordered to stay seventh, penalised for not having maintained reasonable speed under the yellow flags.

Ambrose feels hard done by, but them's the rules and in his heart he knows NASCAR made the correct call.

Once racing resumed he could make up only one place in the remaining five laps.

Johnson admitted his 51st Sprint Cup victory was "a gift".

Ambrose finished sixth. It was a very bitter pill.

In a brief post-race interview he was acutely awkward but wisely bit his tongue.

This had been his biggest and best chance to win in the Sprint Cup.

Almost all NASCAR rounds are on oval tracks, but Sonoma is a road course that gave Ambrose, with his Australian and European road racing background, a competitive advantage.

His previous best finish in the Sprint Cup had been third at this track last year - his first full season in American stock car racing's biggest league and during which he had four other top-five finishes.

But even before yesterday this had been the year from hell for the Aussie abroad in perhaps the most competitive major race series on earth.

Only once in the previous 15 rounds this season had Ambrose been in the top 10 at the chequered flag.

Before Sonoma he talked of how things had gone "pear-shaped" and that he feared for his place in NASCAR every week - and the livelihoods of those who work for his JTG Daugherty Racing team, owned by business couple Tad and Jodi Geshickter and former basketballer Brad Daugherty.

It is a satellite operation under the umbrella of the team of Michael Waltrip, a two-time winner of NASCAR's classic Daytona 500, but not in the league of the teams owned by Rick Hendrick, Joe Gibbs, Jack Roush, Richard Childress, Chip Ganassi and Roger Penske.

Yet the sixth place with which Ambrose emerged from California is his best result of this season and he gained three places in the point standings, albeit only to 27th.

One wonders, though, if the incident for which he has now become most famous in NASCAR may yet work in his favour, a bit like how a rock fall at Bathurst unleashed a wave of sympathy and support for Dick Johnson, who was to become a legendary Australian touring car figure.

Amid all the sniggering post-Sonoma, one NASCAR commentator, Bob Pockrass, has written: "There is something good in all of this for Ambrose.

"Ambrose is a well-liked driver by many fans and competitors.

"He always tries to put a smile on his face and he's truly thankful for the opportunity to race in NASCAR.

"That isn't lost on a fan base that is sceptical about whether all drivers are appreciative of their opportunity.

"If this had happened to Dale Earnhardt Junior or Kyle Busch, the talk would be that this was a gaffe of epic proportions, the result of a lack of focus and the reason why they won't win championships.

"If this had been Jeff Gordon or Mark Martin, there would have been more of a sense of disbelief, but it would have been laughed off as just an unfortunate incident.

"But with Ambrose, it seems as if fans just want to cry.

"They feel so sorry for him. They want to go give him a hug and tell him it'll be OK.

"Ambrose might need therapy after this.

"There's a saying in sports that an athlete must lose first before winning.

"Well, Ambrose has certainly lost one.

"To win, though, he'll need to get over any feeling he has that he got ripped off by NASCAR.

"It made the right call.

"It was Ambrose's decision that was the wrong one."

Ambrose got out of California as quick as he could, notably wearing a plain T-shirt rather than something adorned with the logos of the sponsors he so assiduously acknowledges, into the arms of his wife and two young daughters at "home" in Charlotte, North Carolina.

To help him move on it's a good thing for him there's another Sprint Cup race this weekend, in New Hampshire, and plenty more to come in quick succession.

As hard as it will be to put yesterday's lost golden opportunity behind him, in the weird and whacky world of NASCAR racing, with pile-ups that can eliminate a dozen cars in an instant, Ambrose's luck may yet turn in the States.

And it will be far better for him if it happens to be on one of the oval tracks.

That would be truly making it in America.