Brad Keselowski, provocative on and off the race track, still can be a splinter under a rival’s skin, a stone in a tight shoe, a speck of dust in the eye, a paper cut … in short, an irritant.

That is such an improvement. Only a couple of years ago, more than a few who joust with him at speed regarded the assertive newcomer to NASCAR Sprint Cup ranks as an irredeemably irksome pain in the anatomy.

Keselowski, only 28 but on the brink of a championship at the highest level of his profession, probably would not agree that he has changed that much since he bulled his way onto the scene in 2009. But the perception of him has.

Respect for the Michigan native who talks the talk but also walks the walk may be grudging. But what would be the basis for withholding it? Complaints now, given Keselowski’s success and a less combustible style, would be dismissed as sour grapes.

A 15th-place finish or better Sunday in the season finale Ford EcoBoost 400 at Homestead-Miami Speedway would secure the first Cup title not only for Keselowski but for legendary Roger Penske, owner of the No. 2 Miller Lite Dodge team.

The achievement would be all the more laudable given the rival Keselowski has engaged in a nine-race Chase stare-down to this point without blinking: Jimmie Johnson, a five-time champion with a remote shot at a possible sixth.

On a recent Showtime Inside NASCAR show, Keselowski’s words revealed not only his aggressive approach to the Chase but the shoot-from-the-lip candor that has ruffled feathers on occasion.

He spared no verbiage in expressing admiration for Johnson’s inarguable mastery at the wheel. But in direct response to a question about the most daunting element of challenging Johnson and the formidable No. 48 Lowe’s team, Keselowski said pointedly:

“I think the most difficult part is that he has done this so many times that the competition around him races him as though they’re defeated.”

Keselowski serves as counterpoint. At Texas two weeks ago, while attempting to protect a lead gained by a two-tire gamble on the final pit stop, he banged door-to-door with Johnson at the risk of wrecking both. Johnson prevailed, but Keselowski’s boldness reaffirmed that it’s not in his makeup to defer to the veteran.

Crew chief Paul Wolfe admitted in an off-handed defense of his driver Tuesday, “To be honest with you, that’s the most aggressive I’ve seen Brad all year. … We’ve had fast race cars. He hasn’t had to push issues.”

Indeed, Keselowski has complemented two victories with six other top-10 finishes in the nine Chase races and an 11th in the other.

He turned a seven-point deficit into a 20-point advantage at Phoenix when Johnson, attempting to chase down Keselowski, blew a tire, smacked the wall and finished 32nd.

Surprisingly, long-time adversary Denny Hamlin came to Keselowski’s defense at Texas after several other drivers questioned Keselowski’s daring. “I just thought it was two guys who were really trying to fight hard for a win,” he said. “I think it may have been a championship moment.”

Hamlin went on to call Keselowski “one of the best racers out there” and to conclude, “Really, to me, there’s no resemblance from the Brad before to the Brad now.”

Turn the clock back three years to the 2009 Ford 300 Nationwide race. Hamlin carried out a vow made after the two tangled at Phoenix a week earlier to retaliate. He bumped Keselowski into a spin down the straightaway.