AVONDALE, Ariz.—It would have been easy for Brad Keselowski to wreck Jimmie Johnson at the end of last week's race at Texas Motor Speedway.

Keselowski would have won the race, surged ahead of Johnson in their championship battle and maybe even put enough separation on him to win his first career Sprint Cup title.

But Keselowski said he wouldn't have felt good about winning that way. So he raced Johnson hard—but clean—on the final restart at Texas and wound up finishing second.

Johnson went on to his second consecutive victory, and took a seven-point lead over Keselowski into Sunday's race at Phoenix, the penultimate event in the 10-race Chase for the Sprint Cup championship.

So why didn't Keselowski go for broke?

"Jimmie has never done anything to me to deserve to be raced in that manner," he said. "When I race people the way I race them, I race them off of a code that you know usually exists off how they've started racing me. He never did anything to deserve to be wrecked, that's for sure. I'm not in the habit of just wrecking people just to wreck 'em. Now obviously if somebody does something to push me around, that's a little different."

His record speaks for itself, and Phoenix was the site of Keselowski's first meeting with NASCAR chairman Brian France during his 2009 feud with Denny Hamlin.

Keselowski had staked a reputation as an aggressive driver who was unapologetic for anything he had to do on the track to be successful. He would not back down to anyone, and he had no interest in hearing any sort of lectures about etiquette or respect for veterans.

It was all unfolding in the second-tier Nationwide Series, where Hamlin was moonlighting and could get away with trying to teach a young driver a lesson. It boiled over at Phoenix, where Keselowski twice hit Hamlin's car in retaliation to wreck him.

Hamlin later complained trying to discuss anything with Keselowski was like "talking to the concrete."

Keselowski was summoned to meet before the Cup race the next morning to a 20-minute meeting with France and other NASCAR officials.

Now, three years later, he's in the thick of a championship race and Hamlin himself sees a changed driver.

"He's better. He'll tell you he's better now and, obviously, it's leading to a lot of success," Hamlin said. "I think that Brad (Keselowski) is one of the best racers out there at this point. Not only from the speed that he has, but the ethics in which he races. He's a great guy to race with. Really to me, there's no resemblance from the Brad before to the Brad now."

So much so that Johnson never worried Keselowski would race him dirty on the final two restarts at Texas. The two drivers were lined up side-by-side twice with the win up for grabs, and Johnson knew Keselowski would give him his best shot.

But he didn't think Keselowski would intentionally wreck him.

"I really feel like he was extremely aggressive and had that mindset of going for broke," Johnson said. "But we all evolve as drivers and I think he was more in control of his vehicle Sunday night than he was when he was new to the sport. I've always raced him with a clear mind and not worry. It never crossed my mind that he would make an intentional move to dump me. There are only a few people out there wired like that.

"People race really, really hard and I think Brad did, but to just go in the corner and dump someone, man that is tough to do. Then you play into the karma thing and then there is always next week. I just don't think there are many guys out there that would haul off into the turn and just dump their competition for the championship."

Kyle Busch, who finished third behind Johnson and Keselowski at Texas, had a prime seat for the battle and didn't think Keselowski was a choir boy in the closing laps and could have trouble with other drivers over the next two weeks.

"It seemed like Brad ran Jimmie up the track a little bit and if you're Jimmie Johnson, obviously you feel like you have one over the guy," Busch said. "Jimmie is smarter than that and better than that, where you don't expect that from him. You see, even if you're myself or Tony (Stewart) or somebody else just running around for race wins, guys that are eliminated from the championship, you almost kind of side with a guy who is cleaner (Johnson) than another guy and you'll do anything you can to make that other guy's day hell."

But Roger Penske, Keselowski's team owner, believes his driver has made great strides the last three years and has changed some minds in the industry.

"One of the great things that has happened is Brad has gained the respect of the garage area from the standpoint of the drivers and the teams and obviously the officials," Penske said. "I think that he sees people like Jimmie and Jeff (Gordon), people who are real stars here, and I think he's trying to emulate that on the race track and show how good he is."