Stewart will be competing on the new 2010 Yamaha YZ450F motorcycle and is the first rider to test the machine in race conditions."The bike is different, so it is like making a big change," Stewart added. "I have been riding it for a few weeks and I like it. It was simple to switch, and we will let the racing speak for itself. I feel comfortable, and this will be the first weekend the bike is raced in front of everyone."Stewart capped off a banner AMA Supercross season earlier this year, notching 11 wins en route to the second championship of his career. He’s currently fourth on the all-time AMA Supercross class win list, just two races behind rival Chad Reed. Stewart looks forward to the unique elements that are added into this year’s race."One thing that is cool is that Feld (Motor Sports) has always done a good job with switching things up," said Stewart. "This race is different, which makes it fun. The one-lap races should be fun. There is only one lap in the head-to-head competition, so endurance doesn’t count; it’s about speed and knowing what you’re doing. I’m a racer, and I feel that I can step up to the plate and do it." Villopoto missed most of the AMA Motocross season due to a knee injury, and this will be his first race since the Hangtown AMA Motocross race. During his rookie AMA Supercross class season he finished sixth overall and scored two wins. Villopoto became the first rider in history to beat Stewart in a race that he did not crash in. This will be Villopoto’s debut at the Rockstar Energy Drink U.S. Open. "Last night I decided to race this event around 6pm," said Villopoto. "I have been riding for two weeks and feel really good. I wanted to race to prepare for Anaheim since I have been off most of the summer. I feel really good health wise. I feel good like last year and since I got on the bike two weeks ago".Like Villopoto, Millsaps will make his Rockstar Energy Drink U.S. Open in the premier class. In 2001, he captured the 85cc Mini Invitational as an amateur."This is the first year I had a chance to come back and race the U.S. Open," said Millsaps. "I’m excited and ready to have fun. It’s a tight course and it’s hard to pass, and I am pretty wide."Tickets for the 2009 Rockstar Energy Drink U.S. Open are available at Ticketmaster locations, Carter Powersports (located at 6275 South Decatur Blvd. Las Vegas, NV 89118) the MGM Grand Garden Arena box office, www.ussx.com or by phone at (800) 745-3000.