What was supposed to be a season-ending showdown at Las Vegas Motor Speedway became instead a script for disaster Sunday: a fiery 15-car crash that killed popular two-time Indianapolis 500 winner Dan Wheldon and left the shaken auto racing community to deal with uncomfortable questions.

The drivers knew the Las Vegas race was going to present challenges even before the season began.

The sleek, open-wheel machines of IndyCar had not raced at the track since 2000, and the now-defunct Champ Car Series was last there in 2005. Some of the drivers had been there before, but many had not. None had raced an IndyCar there since the track’s 2006 reconfiguration added “progressive banking’’ designed to increase side-by-side racing.

So there was some initial fretting when second-year IndyCar chairman Randy Bernard announced a $5 million payday to any moonlighting driver who could win the race.

Bernard had hoped to land a superstar or two from the fender-rubbing NASCAR circuit. Maybe even former Indianapolis 500 winner Juan Pablo Montoya.

But nobody bit, despite interest from NASCAR driver Kasey Kahne, X-Games star Travis Pastrana, and former CART champion Alex Zanardi.

“Hopefully they’ll pick someone competent enough to drive those things because it is an IndyCar,’’ Penske driver Will Power said shortly after the prize was announced. “You can’t rub panels. You rub wheels, and someone’s going flying.’’

Kahne said yesterday that team owner Rick Hendrick was against his participation, and Hendrick confirmed it. Kahne’s lack of experience in an IndyCar made it virtually impossible for him to win.

That left only Wheldon, winner of 14 races on ovals in IndyCar, including the Indy 500 in May, to be eligible for the $5 million prize. Bernard made that ruling because the 33-year-old Englisman lost his job at the end of last season, put together a one-race deal for the Indy 500, and had turned down other offers.

Wheldon put together a deal with Sam Schmidt Motorsports to race two weeks ago at Kentucky and for the prize Sunday.

“He wanted to do it in the worst way,’’ an emotional Bernard said yesterday.

Interest in the final race, which Bernard had worked tirelessly to create, had risen enough that sponsors wanted to get involved. Because IndyCar is in the final year of racing its current car design, teams had expendable inventory.

It led to 34 entries in the field. That’s one car more than the Indy 500. Who were these new drivers? Competitors without much experience at IndyCar’s top level.

It was the fourth start for Wade Cunningham, who was in the thick of the action where the accident started.

It was the third career start for Pippa Mann and the 20th for JR Hildebrand, who both spent Sunday night in a Las Vegas hospital recovering from injuries suffered in the accident.

At least six drivers didn’t have enough starts to complete a full season, and some of the veterans had raced only a handful of times this season.

They all turn out for the Indy 500, too, and the speeds on that oval are faster than they were at Las Vegas. But Indianapolis is a relatively flat track, is a mile longer than Las Vegas, and drivers have three weeks of track time to prepare for the race.

The drivers had 3 hours, 15 minutes of practice time over three days to get ready for Las Vegas. They were not on the track at all Saturday.

Davey Hamilton alluded to a lack of experience contributing to Sunday’s accident.

“You can’t come in here and race with these guys and think you’re going to beat them - ever,’’ Hamilton said.

Sitting at home, five-time defending NASCAR champion Jimmie Johnson watched the accident in horror. Yesterday, he urged IndyCar to stop racing on ovals.

“I hate, hate, hate that this tragedy took place. But hopefully they can learn from it and make those cars safer on ovals somehow,’’ he said.