After he won his first NASCAR Sprint Cup championship in 2006, Jimmie Johnson went from being the hunter to the hunted.

And for five long seasons, he rebuffed every attempt to knock him off the top rung of NASCAR in a remarkable run that likely never will be equaled again. In the first six years of the Chase for the Sprint Cup, Johnson won 18 of 60 Chase races, a remarkable 30 percent winning average.

But in the last couple of years, Johnson has looked mortal in the Chase. Although he won a fifth title in 2010, Johnson won only one Chase race that season. Last year, when he was finally dethroned by Tony Stewart, Johnson also won only one Chase race.

And this year, he’s 0-3, albeit with three top-five finishes, including two runner-up runs.

Johnson’s winning percentage in the Chase is all of a sudden down to 24 percent. Still excellent, of course, but well off what it once was.

More troubling, perhaps, are the events of this season.

In the opening race of the Chase this year at Chicagoland Speedway, Johnson led 172 of 267 laps, but had nothing at the end for Brad Keselowski, who ran away late and won, while Johnson finished second.

At Chase race No. 2, Johnson again finished second but wasn’t even in the same zip code with race winner Denny Hamlin, who led 193 laps in his Joe Gibbs Racing Toyota to Johnson’s two laps led in his Hendrick Motorsports Chevrolet.

Sunday at Dover International Speedway, a place where Johnson has seven victories and had led 2,275 laps coming into the race, he watched Keselowski win again. Meanwhile, the JGR Toyota of Kyle Busch led 302 laps and Johnson had to save gas to bring his No. 48 Hendrick Chevy home in fourth place.

Mind you, Johnson is still deep in the thick of the title hunt, just five points behind Keselowski and 11 ahead of Hamlin. He’s not in a bad spot right now.

Then again, this week, the Sprint Cup traveling circus heads to Talladega Superspeedway for Sunday’s Good Sam Roadside Assistance 500. And has been well-documented this year, Johnson has failed to finish any of the three prior restrictor-plate races run this season, losing an engine in the first Talladega race and getting wrecked twice at Daytona.

“Well, as you can probably see from our finishes this year, we haven’t had a lot of luck at the restrictor-plate tracks,” said Johnson. “It definitely is the one track in the Chase I’ve kind of been a little concerned about. There are a lot of great tracks for the 48 coming up in the Chase, but this one is definitely one where anything can happen.”

The reason is simple enough: At restrictor-plate tracks, drivers are at the mercy of others: Who’s pushing them, who’s wrecking around them, who’s doing what in the draft. It’s an uncomfortable state of affairs for drivers who like to be in charge of their own destiny.

“There are so many things that are out of your control,” said Johnson. “There is a lot of room on this track to move around, though, obviously, and try things. I think the odds are in our favor to be able to finish one of these restrictor-plate races this year. At least I hope so.”

By the end of Sunday afternoon, Johnson will know the answer.

He’ll also have a pretty good idea about his odds for a sixth championship by the time checkered flag falls at Talladega. A lot can happen there. Whether for Johnson it turns out to be good, bad or indifferent is just a matter of time.

Tom Jensen is the Editor in Chief of SPEED.com, Senior NASCAR Editor at RACER and a contributing Editor for TruckSeries.com. You can follow him online at twitter.com/tomjensen100.