CONCORD, N.C. — It's not that common for siblings to reach the highest level of a professional sport, and when it happens, one of them typically toils in the shadow of the superstar.

That's been the case the past five years in NASCAR, where the Busch Brothers were never in the same league.

Big brother Kurt hit his peak in 2004, when he won his only NASCAR championship, but his results were up-and-down after that banner season. Then along came Kyle, seven years his junior and a headline maker from the very beginning.

When Kyle raised his game in 2008 to become a title contender, Kurt was off the pace and searching for solutions. When Kurt turned it around and climbed back into the Chase for the Sprint Cup championship last year, Kyle was in a slump that led to the late-season firing of his crew chief.

After five years competing against each other in NASCAR's elite division, the early hopes of a bitter championship battle between brothers had faded.

My, how things have changed.

The Busch Brothers are finally running at the same level, setting up a potential sizzling showdown over the upcoming long summer stretch of racing.

Kurt Busch completed a two-week sweep of Charlotte Motor Speedway on Sunday night, closing out the first win for team owner Roger Penske in the prestigious Coca-Cola 600 eight days after claiming the $1 million prize in the annual All-Star race.

Kyle Busch, meanwhile, won the Nationwide and Trucks Series races at CMS over the last two weeks, plus the Nationwide and Sprint Cup Series races at Dover earlier in May.

All told, the Busch Brothers have won the last six races spanning NASCAR's top three series. The lone NASCAR celebration not by a Busch was Martin Truex Jr.'s victory in the Sprint Showdown, an All-Star race qualifier without either brother.

"That's kind of cool," Kyle Busch said of the family domination.

Indeed it is, particularly considering how combustible these two drivers are — particularly when racing each other.

Nobody has forgotten the 2007 All-Star race, when hard racing between the two led to an accident that knocked two of the strongest cars out of the event. They were furious with each other following that May accident, and it wasn't until their grandmother insisted they make peace or risk ruining Thanksgiving dinner that the hardheaded racers resolved their dispute.

That's right, brothers who passed each other every week in the garage, the motorhome lot and on the track went six months without speaking over an accident in a non-points event.

That was three years ago, and while not much has changed with either Busch's style — they are both still aggressive, highly focused and often hot-tempered in the race car — they have both gotten smarter.

Kurt, now 31, is showing the wisdom that compliments his talent level.

Although there were flashes of growth over the past few years, it was punctuated late last season when he hung strong in the Chase even after crew chief Pat Tryson announced he was leaving at the end of the season. He admitted after Sunday night's win that his personal progress was made after realizing the mistakes of his youth.

"I'm not one to go out there with a big flash and a big flare," he said. "I used to early on. I'd run my head up against the wall. I'd run my race car up against the wall. Reviews came in negative. For me, that's not how I wanted to be remembered."

And he didn't hesitate in choosing Steve Addington, who was fired in October by Kyle Busch, as his new crew chief. Since taking over the No. 2 Dodge this season, Addington has guided Busch to two points wins, the All-Star race victory, and seven top-10s in 13 races.

"What I really enjoy about Steve is the confidence he gives me in the car and the adjustments that he makes," Kurt Busch said. "I feel like he's helped me pick up my game because I have to have a fresher outlook on different setups."

Kyle, who just turned 25, is still a work in progress. His raw talent has never been questioned, but his decision-making isn't always the best, particularly when he can smell victory. He wrecked out of last week's All-Star race when he and teammate Denny Hamlin raced each other hard in the closing laps, and a furious Jeff Burton confronted him following the 600 to discuss how aggressive Kyle Busch had been on the final restart.

Hamlin chided his teammate last week as being too immature to win a Cup championship, and Kurt Busch seemed to agree when he wondered if his younger brother shouldn't have backed down in the All-Star race.

"He's been running these All-Star races for a few years now, running at a 1,000 percent pace every year," Kurt said. "It doesn't take a 1,000 percent pace to win it."

Maybe Kyle Busch figured that out over the weekend, when he came from two laps down to win the Nationwide Series race and overcame a pit-road disaster while leading the 600 to rally for a third-place finish.

"These are the kind of races that make a championship," he said after the 600.

If he's right, and both Buschs are involved, it could be a very exciting time for NASCAR.