Italian Honda rider Marco Melandri claimed his first MotoGP victory in perfect style at the new Istanbul Park circuit yesterday, with a convincing defeat of world champion Valentino Rossi.

The 23-year-old from Ravenna, 250cc champion in 2002, led off the line for the first of 22 laps of the 5.34-km circuit and was headed for only two laps, by his team-mate Sete Gibernau until the Spaniard briefly ran off the track.

Rossi moved into second place after eight laps, about one second behind Melandri, but could not match his younger compatriot's pace and Melandri gradually stretched away to win by 1.513 seconds.

"It's an unbelievable day for me," Melandri told reporters. "Rossi was close but I tried to keep my rhythm and, after a bit, Valentino started to lose a little lap by lap."

Rossi, who has one more chance to break his own record of 11 victories in one season, said: "I'm happy with second. We struggled a lot this weekend."

American Nicky Hayden was third, with Gibernau fourth and Ducati's Carlos Checa fifth.

Melandri, a close second to Gibernau in qualifying, has been threatening to win since finishing second to Rossi in the Dutch TT at Assen in June.

He was also ahead of Rossi in Japan when the pair collided, leaving Melandri with foot injuries.

Australian Casey Stoner (Aprilia) claimed a narrow victory over world champion Dani Pedrosa (Honda) of Spain in the 250cc race.

Frenchman Mike Di Meglio (Honda) won his first race in the 125cc class. Points leader Thomas Luthi (Honda) of Switzerland was fifth, not enough to secure the title even though his only rival, Finn Mika Kallio (KTM), crashed out of the lead on the final lap.

Motogp Standings (leading): 1. Rossi (Yamaha) 351; 2. Melandri (Honda) 195; 3. Hayden (Honda) 186; 4. Edwards (Yamaha) 171; 5. Biaggi (Honda) 163; 6. Gibernau (Honda) 150; 7. Capirossi (Ducati) 148.