World champion Valentino Rossi has once more powered his way into the record books with victory at the Australian Grand Prix.

The Italian took the chequered flag almost 10 seconds clear of Alex Barros for his 50th career win.

By winning his 11th race of the season, the 23-year-old became only the sixth rider to record a half-century of GP wins.

Afterwards he said: "This year is incredible - 50 victories is like a dream."

More records are looming for Rossi, who has the opportunity to pass Michael Doohan's current best of 12 victories in a season in Spain on 3 November.

Currently on 335 points for the season, he is just five points shy of Doohan's world record tally for a season.

Barros had looked on course for the win, though, leading for much of the race before Rossi took his opportunity to pass late on.

The Brazilian rider explained: "He (Rossi) rode behind me for 25 laps. I tried to overtake him (on the final lap) and I braked too hard.

"I'm a bit disappointed to arrive at second place like that."

Meanwhile, Marco Melandri, edged out Fonsi Nieto to win the 250cc race and become the youngest ever world champion in the class.

The 20-year-old beat the previous record set by compatriot Rossi, who was 176 days older when he won the 250cc title back in 1999.

Melandri was neck-and-neck with Nieto on the final lap and held him off by just 0.007s in the home straight.

The new world champion said: "It was an unbelievable race."

Australian MotoGP results:

1. Valentino Rossi (Ita) Honda 42mins 02.041s
2. Alex Barros (Bra) Honda 42:11.823
3. Tohru Ukawa (Jap) Honda 42:13.175
4. Daijiro Kato (Jap) Honda 42:13.368
5. Jurgen v.d. Goorbergh (Ned) Honda 42:13.455
6. Max Biaggi (Ita) Yamaha 42:22.978
7. Nobuatsu Aoki (Jap) Proton 42:24.546
8. Olivier Jacque (Fra) Yamaha 42:28.683
9. Kenny Roberts (USA) Suzuki 42:28.733
10. Jeremy McWilliams (GBR) Proton 42:34.035