It’s hard to wipe the smile off Tony Stewart’s whisker-covered face these days.

Since failing by just 16 points to make it into NASCAR’s Chase for the Nextel Cup championship — relegating him to a season finish no better than 11th — the two-time series champion has been on a roll.

He’s won three of the eight Chase races so far, including the last two in a row, and has honed his flagstand-climbing celebrations to near perfection.

“I’m having fun and the team is having fun,” Stewart said after his dominating victory last Sunday at Texas Motor Speedway, where he led 278 of 339 laps. “How can you not have fun when you’re winning?”

It didn’t look like Stewart was going to be enjoying himself much after the Richmond race in September, where he finished 18th and barely was eliminated from title contention.

The burly Stewart can be a teddy bear and a lot of fun when things are going well. But he also can be angry, sarcastic and difficult when the going on the racetrack gets tough. His past difficulties with other drivers, the media and even fans is well documented.

But this 35-year-old version of the Indiana native is different from the Stewart of the past.

It began last year when he was virtually unflappable on the way to his second Cup title, shrugging off the inevitable disappointments throughout the long season.

During the Richmond race, as Stewart flirted with making the 10-man Chase field and then came up short, there was much speculation that he either would bolt without comment — as he has done on occasion in the past after a particularly disappointing race — or do his impression of a volcano erupting when asked questions he often considers stupid.

Instead, Stewart was a perfect gentleman, praising the drivers who beat him out and accepting his fate with a shrug.

And his No. 20 Joe Gibbs Racing team, led by longtime crew chief Greg Zipadelli, went right along with the program, simply packing up after Richmond and starting preparations for the new week at New Hampshire without looking back.

Stewart finished second that week, a sign of things to come in the Chase.

Not every race since then has been great — he’s had finishes of 33rd at Dover and 22nd at Talladega. But Stewart has five top fives in the eight races, including wins in Kansas, Atlanta and Texas and a fourth at Martinsville, and has racked up more points than any driver in the Chase.

“There’s just a lot of pressure and a lot of stress involved in trying to win a championship at this level,” Stewart explained. “That’s the goal that everybody wants and, in my opinion, it’s the biggest championship in the United States to win right now.

“Obviously, when you’re in it, it’s harder to keep yourself in this frame of mind. But I think this frame of mind started because we needed to keep the team pumped up. We had never finished worse than seventh (in the points) and were obviously all devastated. None of us would have dreamed that we would miss the Chase.”

Jimmie Johnson, leading the playoffs by 17 points over Matt Kenseth, has finished second to Stewart each of the last two weeks and says he isn’t surprised to see “Smoke” burning up the tracks.

“He’s a champion, and just because he missed the Chase — which was a shock to everybody — he wasn’t going to stop racing as hard as he always does,” Johnson said. “He had something to prove to himself and everybody else, and that’s just what he’s doing.”

Someone pointed out to Stewart during the postrace news conference at Texas that he has the opportunity to win out at Phoenix and Homestead the next two Sundays and finish the season with a career-best seven victories. He won six times in 2000, his second season in Cup, and has a total of 29 wins.

“That’s a great goal,” Stewart said, his eyes lighting up. “But, trust me, we would all trade these race wins in and everything to be just back in the Chase right now.”