The spectre of a surging Valentino Rossi will loom large for MotoGP world championship leader Nicky Hayden at this weekend's Japanese Grand Prix.

World champion Rossi sliced five points off Hayden's lead in Australia, moving him within 21 points of the Honda rider with three races left.

"A gap of 21 points is still a lot but it's not impossible," said Rossi. "We have three races left. We have to try to get more points from Hayden in order to stay in the fight."

Five-times top class champion Rossi snatched third for Yamaha by darting past Spain's Sete Gibernau at the death last Sunday, while Hayden could finish no better than fifth despite starting on pole.

But Rossi's aversion to the Motegi circuit will offer Hayden a ray of hope as he tries to fight off the Italian's charge.

"Honestly, it's not a track I like very much," acknowledged Rossi, who failed to finish last year after colliding with Marco Melandri.

"But I think we're going there in good shape so hopefully we can go back to Europe with an even better shot at the title."

Hayden paid tribute to Rossi's bold move on Gibernau, admitting it could prove crucial in the title run-in with only races in Portugal and Spain to come after Sunday's race.

"It was looking okay until Rossi got Sete in between us, which was not great," said the American. "But we're still holding on with three races to go. We'll just roll into Motegi and keep fighting."

Hayden has 225 points with Rossi on 204 while Honda's Melandri kept his outside title chances alive by winning in the pouring rain at Phillip Island last weekend.

The Italian's win gave him a share of third place in the standings on 193 points along with Honda's Dani Pedrosa of Spain. Ducati's Loris Capirossi is a further 13 points adrift.

Capirossi stormed to victory in last year's Japanese Grand Prix after starting on pole, setting a lap record in the process, and could still have a say in who wins this season's title.

Spain's Jorge Lorenzo extended his lead in the 250cc championship with his fourth win in five races for Aprilia last weekend.

Lorenzo has 249 points with Honda's Andrea Dovizioso on 225 after the Italian slipped to fourth following a superb start.

The 125cc title was decided in Australia when Spain's Alvaro Bautista powered to his seventh victory of the season.