Valentino Rossi got his 500cc MotoGP title defence off to the best possible start with a win in the season-opening Japanese Grand Prix.

Rossi, on a new four-stroke machine, had taken pole despite being dominated by Loris Capirossi's two-stroke in early practice.

But four-strokes dominated, with second-placed Akira Ryo on a Suzuki, and third Carlos Checa on a Yamaha also on the new machines.

Honda rider Rossi said: "This is a special moment for me as this is the first race of a new series.

"Also, this victory is more important than normal for me because on Friday and Saturday I crashed in the build-up.

Miyazaki wins 250cc

"I made a good start and was always in the first group. It was difficult to overtake for a long time but on the last lap I made no mistakes and was able to win.

"Four strokes are very different," added Rossi.

"With our bike it is difficult to control when you open the throttle but our top speed is better than Suzuki's, so I got past Ryo at the end of the chicane."

With his fifth straight victory, Rossi becomes only the sixth rider ever to take five or more consecutive wins in 500cc.

Italy's Max Biaggi, last year's runner-up in the season standings, crashed out on the sixth lap and was unable to continue.

Exciting teenager

American Kenny Roberts also lost control of his bike on the sixth lap and didn't finish.

Japan's Osamu Miyazaki took the 250cc race on a Yamaha.

He beat compratriot Daisaku Sakai who rode a Honda, and Randy de Puniet on an Aprilia.

French rider Arnaud Vincent withstood a late charge from defending champion Manuel Poggialli to take the honours in the 125cc race.

The Aprilia rider started from the fourth row and completed the 18 laps in 46 minutes, 22.971 seconds.

Italian Mirko Giansanti, on a Honda, finished second, 1.16 seconds behind Vincent with Poggialli, the San Marino teenager in third.

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500cc results
1. Valentino Rossi (Ita) Honda 49 minutes, 32.766 secs
2. Akira Ryo (Japan) Suzuki 49:34.316
3. Carlos Checa (Spain) Yamaha 49.41.119
4. Shinichi Itoh (Japan) Honda 49:43.595
5. Norick Abe (Japan) Yamaha 49:53.189
6. Alex Barros (Brazil) Honda 50:05.025
7. Nobuatsu Aoki (Japan) Proton KR 50:12.399
8. Regis Laconi (Fra) Aprilia 49:40.232 one lap
9. Loris Capirossi (Ita) Honda 49:44.518 one lap
10. Daijiro Katoh (Jap) Honda 49:46.895 one lap

250cc results
1. Osamu Miyazaki (Jap) Yamaha 47 minutes, 09.454 secs
2. Daisaku Sakai (Japan) Honda 47:16.395
3. Randy De Puniet (France) Aprilia 47:38.474
4. Emilio Alzamora (Spain) Honda 47:54.754
5. Sebastian Porto (Argentina) Yamaha 47:54.949
6. Naoki Matsudo (Japan) Yamaha 48:04.179
7. Choujun Kameya (Japan) 48:10.026
8. Roberto Rolfo (Italy) Honda 48:11.741
9. Alex Debon (Spain) Aprilia 48:27.736
10. Franco Battaini (Italy) Aprilia, 48:28.831

125cc results
1. Arnaud Vincent (Fra) Aprilia 46 minutes, 22.971 secs
2. Mirko Giansanti (Italy) Honda 46:24.135
3. Manuel Poggiali (San Marino) Gilera, 46:25.529
4. Noboru Ueda (Japan) Honda 46:26.450
5. Simone Sanna (Italy) Aprilia 46:33.159
6. Shuhei Aoyama (Japan) Honda 46:46.027
7. Angel Rodriguez (Spain) Aprilia 46:46.624
8. Daniel Pedrosa (Spain) Honda 46:56.459
9. Lucio Cecchinello (Italy) Aprilia 46:57.258 10. Gino Borsi (Italy) Aprilia 47:10.275