Valentino Rossi became only the second rider in history to regain the MotoGP World Championship after two successive defeats, when he won his sixth premier-class title with victory in Yamaha's home Japanese Grand Prix at Motegi on Sunday.

Rossi needed to finish third or better, even if nearest rival Casey Stoner won, to lift the championship three rounds early - but the 29-year-old Italian exceeded those requirements by charging from fifth on lap one to overtake leaders Dani Pedrosa and then Stoner by lap 14 of 24.

The Italian went on to claim his eighth world championship over all three classes by almost two seconds from the Ducati rider, while fourth for team-mate Jorge Lorenzo helped complete the triple crown of Rider, Manufacturer and Team titles for Yamaha.

"It's a great victory and a great achievement," smiled Rossi. "The race was a great battle and I had to ride at 100%, like I have through all through the season! Pedrosa and Stoner today were very strong and it was fun to fight with them like this, I am happy that it was a good race for the fans. It was a fantastic feeling to take the title with a win, like I did in 2001 and 2004."

Rossi's sixth world title leaves him behind only Agostini (eight premier-class titles) in the all-time standings and he marked the achievement with a special post-race celebration.

"The show after the race was one of my friends pretending to be a 'notary', signing and certificating the eighth championship 'deed," explained Rossi. "It was very exciting to be planning the championship t-shirt and celebration once again with my friends and fan club and the one we came up with is funny I think, it says 'I'm sorry for the delay!' "

Rossi was unbeaten in the premier-class from 2001 to 2005, winning the final 500cc crown and first two MotoGP titles for Honda, before a sensational switch to Yamaha saw his title run continue for a further two seasons.

But his dream run came to an end in 2006 when accidents, technical problems and bad luck - combined with a consistent attack from Nicky Hayden - saw the Honda rider claim the final 990cc crown. Things got worse in 2007, when Stoner and Ducati destroyed the opposition during the first year of 800cc competition, while Rossi and Yamaha slumped to third.

Rossi demanded improvements from Yamaha and a much improved 2008 spec YZR-M1, combined with Rossi's winter switch from Michelin to Bridgestone tyres, resulted in victory at round four of the 2008 season.

"The decision to change to Bridgestone tyres, which I took together with Jeremy [Burgess], my team and all the Yamaha crew, was very important, as were the changes to the bike because the first 800cc M1 last year was not competitive enough," confirmed Rossi.

"We spoke a lot during last season and I remember a strange meeting in Valencia last year, me with a broken hand, speaking with [Yamaha technical boss] Furusawa about 2008. From then we started to work on the improvements for this season. It's also been important to have the right people in the right place and this year everything has been correct. It's been step-by-step."

After his debut 2008 victory in China, two further wins followed in as many starts, before Stoner and Ducati began a three race run of total domination. Rossi became increasingly worried, hustling the Australian into a mistake - which the #1 went on to repeat while leading at the next two rounds.

Rossi has been unbeaten ever since Laguna Seca, winning eight of the 15 rounds so far and, with three remaining, is still in with a chance of matching the eleven he won with Yamaha in 2005. Sunday's win was also Rossi's 70th in the premier class, his 96th in total and his 148th career podium.

"I think I have made a lot of good decisions this year and we have been competitive from the start," reflected Rossi. "Qatar was the worst race of the season but I knew our potential was good so, although we were a bit worried at that point, we weren't desperate because we knew if we fixed a few problems we could try to win.

"At the beginning of the year we had some important results when Bridgestone wasn't the strongest: Jerez, Portugal and others, and in that period we took a big advantage from Stoner. After Barcelona Casey started to ride like a demon and dominated three races in a row, and then we went to Laguna which was the turning point of the season. Laguna was a real battle and from then on we have flown.

"I think it's difficult to say, but maybe this is even better than the first championship with Yamaha in 2004. In 2004 I arrived after three championships in a row; the change was very big and no one expected me to win then, not even us to be honest! But this year is great too because I didn't start as the number one favourite after losing for two years. The taste of this is something special.

"In 2006 I lost because of bad luck; I still won the most races and was the fastest on track for most of the time, but in 2007 Stoner was a lot faster than us and so we got to the end with a big of disadvantage. Winning this championship was very difficult but also very, very important."

When asked how the disappointments of the previous two seasons have changed him, Rossi was typically honest.

"I grew up a lot in the last two years, because at the end of 2005 I had a great career and I had won all the important targets so far," he said. "125, 250 and then five titles in a row in MotoGP with two different bikes - I felt unbeatable. But in 2006 and 2007 I learnt to lose and this has been very important. I came out much stronger and my level of concentration and effort to win this championship has been higher than ever before."

Looking back at his extraordinary premier-class career, Rossi believes - with hindsight - that he could have won the title on his 500cc debut in 2000, whilst naming Stoner as the toughest of the opponents he has faced.

"In 2000, maybe, I could have won on my debut, but I underestimated myself!" Vale smiled. "In 2001 it was the last chance for me to win in 500, so I gave it my best and did that. In 2001 it was the year of the battle with Biaggi, in 2002 it was the year when everybody said that I won because of my bike, then 2003 was the year of Gibernau, it was hard until the end. They were fantastic years but with Yamaha it is different. I enjoy it more.

"During 2003 I started thinking about Yamaha. Of course I was scared about the new challenge, it was a big question mark. This year, when I tested the new bike and the new tyres, I understood that I could win. In 2004, however, when I tested the new bike I understood we had to work a lot. Sincerely, the feeling of winning in Welkom in 2004 was the strongest emotion of my career; more so than in Laguna Seca this year. The 2005 M1 was very fast and that one and the 2008 one are the best Yamaha bikes ever.

"I think Stoner next year will be back stronger again, so maybe he is the hardest rival I have ever had, more than Gibernau and all the others I fought against in the past. Last year I was sorry that after so many successful years, some people thought Valentino was finished and Casey was the new Valentino. As I said, until I stop riding a bike, my objective will always be to win. I like this life and I always try to do my best in it."

Rossi has already signed to remain in MotoGP with Yamaha for a further two seasons.

"I am very content at Yamaha and this is why I signed for two more years," said the #46. "I had some good offers at other factories, but I already changed bike once and proved everything I wanted to and so there is no need to do that again. Also I am no longer 20 years old and I need a good atmosphere in my team in order to keep me focused and happy, and I have this at Yamaha. The atmosphere in our team, from the Japanese all the way down to the garage is fantastic and this is what makes me want to stay."

With 37 wins, Rossi has now had more success with Yamaha than any other factory in his career - Rossi rode for Aprilia in the 125 and 250cc classes as well as Honda in MotoGP - and is also Yamaha's most successful rider, having scored 13 more premier-class wins for the factory than 'king' Kenny Roberts.

"I am so happy that I have now won three titles with Yamaha because this is how many I won with my last team and I want Yamaha to have the same merit - I am a Yamaha rider and I feel different with Yamaha than with anyone else before - I hope we will have more together!" he smiled. "Now I have to get used to being world champion again!"

Rossi believes he is now riding better than at any point in his grand prix career, but forecasts an even tougher title fight in 2009.

"I think 2009 will be even more difficult than this year," he said. "Now I am the world champion again and I have demonstrated that I am still very fast. I think I rode the best of my career this year apart from the mistake in Assen, but next year is another story, it depends on how the winter is and how Stoner, Pedrosa and also Lorenzo are next year, as well as the other riders because there are many fast people in this championship. I think it will be a great championship and I'm looking forward to it, but first I want to finish this year and try to win the final three races!"

And what of the long term future?

"As I said, there are many strong riders but of course I hope that in the future nobody will win like Valentino Rossi!" he declared. "Maybe my brother Luca will be as strong as me... I wanted to take him on my bike on the celebration lap, but they did not allow it.

"Maybe I will wait for him to be a MotoGP rider before quitting, then I will beat him in the first year, and then I will stop riding!"

Rossi is due to ride an early version of the 2009 YZR-M1 at Motegi on Monday, before heading for next weekend's Australian Grand Prix at Phillip Island.