LAS VEGAS -- Team Suzuki's Ricky Carmichael will defend his 2005 title at the eighth annual Rockstar Energy Drink U.S. Open at Las Vegas' MGM Grand Garden Arena today through Sunday. The events start at 7 p.m. each day.

For the first time in history, Carmichael, who has won an unprecedented 15 AMA National championships, and James Stewart, who is the reigning Amp'd Mobile World Supercross GP champion, will race against one another.

Carmichael, of Tallahassee, Fla., has won three U.S. Open titles -- more than any other rider in history-- and is this year's defending champion.

In last year's showdown, Carmichael won both nights of racing, besting 2003 and 2004 champion Chad Reed.

"The U.S. Open is a special race for me," said Carmichael. "Last year when I won the U.S. Open, it capped off my best season ever as I won the World Supercross GP, AMA Supercross and AMA Motocross championships. There will be an exciting new format this year that offers all of us a chance to win a lot of Live Nation's money."

At 26, Carmichael has established himself as the world's greatest motocross racer with 15 AMA National championships. The Factory Suzuki rider won his fifth Amp'd Mobile AMA Supercross championship in May and clinched his 10th AMA Motocross championship this summer.

Built into this year's Open format will be the three part Toyota Trifecta bonus program that will pay additional money to the fastest qualifier for each night's event, a bonus to each night's Progressive Direct Holeshot winner and a bonus for any rider that can complete the Toyota Trifecta challenge by being the fastest qualifier, getting the Progressive Direct Holeshot and winning the main event.

Any rider that hits the Toyota Trifecta will earn a $50,000 bonus each night in addition to the regular event purse and any rider that can "Double Down" and hit the Toyota Trifecta both nights will walk away with $250,000 for the weekend.