Rossi says 2008 title his hardest effort

The Italian, who last won the title in 2005, came from behind to beat title rivals Casey Stoner and Dani Pedrosa to victory at Motegi, claiming the title with his fifth consecutive race win and his eighth in 15 rounds this season.

Although Rossi said it was hard to compare his championships, he admitted that he had worked particularly hard for this year's triumph.

"It's difficult to say, but for sure this one is great," he said.

"I feel very good because the battle this year was very tough, especially with Stoner and Pedrosa. It was a long season with a lot of hard racing and hard battles.

"I'm so happy. In my career I've been lucky - I've won a lot of good and difficult championships, like the first one with Yamaha in 2004, but I think this one is the one I put most effort into trying to win. I worked a lot in the weekends of the races, but also away from the races I tried to always stay concentrated and very strong."

Rossi paid glowing tribute to both his Yamaha team and Bridgestone, having switched to the Japanese tyres from long-time supplier Michelin at the end of 2007.

"I have to say a great thank you to Yamaha, who worked a lot, especially Masao Furosawa," he said.

"Great effort from them. The M1 this year is very fast at every racetrack.

"I have to say thank you to Bridgestone and to all my team, from Jeremy Burgess to all the guys, because I think we deserve this championship. We were very strong every weekend and we were fast."

He added that it was particularly satisfying to secure the championship with a hard-fought race win, having charged up the order from an early fifth place.

"I'm also happy because today was a great battle and a great race," said Rossi, who only needed a podium finish to clinch the title today.

"I felt confident with the bike and to win the championship with a race win is fantastic."