Josh Grant made a stunning impact on his Yamaha AMA Supercross class debut by winning the 2009 Anaheim season opener, after a collision between title favourites Chad Reed and James Stewart.

Defending champion Reed and former champion Stewart have both changed seats during the off-season - Reed joining Suzuki and Stewart taking the Australian's place at L&M Yamaha - but the came close to a literal seat swap when race leader Stewart appeared to miss a gear and was rammed from behind by Reed.

Reed then mounted a charge back through the pack to take third position but Stewart, unable to restart his machine, was T-boned by Kevin Windham an forced to retire.

"I got the holeshot and uncharacteristically I let him [Reed] go by. I was making a few mistakes in the beginning and I wasn't really comfortable yet. He ended up getting by me and actually pulled away," recalled Stewart. "I found my rhythm and came back up and he might have started fading a little bit - I don't know what he was doing - but I went past him pretty quick and then I came into that corner and I missed a shift. Once I clicked back in, all I know is - just like Toronto in 2006 - I was getting hit from the rear. He took me out and I was down and out, and couldn't start my bike again."

"I went to second place right away [in the main event], and I felt like I had some better lines than the [Stewart]," said Reed. "When he made a mistake, I got by him and tried to put my head down but he got back by me. Then, I was getting ready to pass him back when I think he missed a gear and we both went flying. We bent the bike up pretty good and I lost the front brake so I'm pretty excited to be on the podium. It's a shame that we crashed because I think we would have had a good battle. I felt like I had a win in me, for sure."

Grant was running in third position prior to the Stewart-Reed incident and fronted the pack for the rest of the race for a sensational debut result in his first meeting in the Supercross category since joining Joe Gibbs Racing Yamaha during the winter.

"I just kept plugging away and I didn't even look at the board or the laptimes or how many laps were left. I just kept going and when it felt like halfway I looked up and it said '18 laps' and I was like, 'Thank God!'" said the young Californian, who had to nurse his machine across the line after catching a trackside banner in his rear wheel with two laps remaining. "I'm just so pumped, and I didn't want to take too many chances with the banner in the wheel, so I just kept riding and it came through."

Standing between Grant and Reed on the podium was Honda's Andrew Short.

The AMA Supercross Lites event was won by Jake Weimer with fellow Kawasaki rider Ryan Morais second and Suzuki's Ryan Dungey third. Jason Lawrence, returning after suspension, took fifth.

Round two takes place in Phoenix on January 10.