Stoner now holds a 10-point lead over Rossi in the standings

The Australian won in 42 minutes 2.85 seconds to move 10 points clear of Rossi, who was 10th after appearing to struggle with a rear tyre problem.

Spain's Tony Elias took second for Honda while Stoner's Italian team-mate Loris Capirossi finished in third.

A big collision on lap one saw Colin Edwards and Dani Pedrosa crash out.

Rossi started on pole but his race plan was upset when he veered off during an early turn into the grass.

The Italian five-time world champion tenaciously fought his way back up to second behind Stoner with 14 laps to go but fell back out of contention.

Once in front I just went into a mental blockout for the next two laps and that enabled me to stay focused Casey Stoner

"We are very disappointed because we had high expectations, but instead we had some unexpected problems with the tyre and it's been a disaster," said Rossi.

He also criticised the riding of Elias.

"I'm also quite unhappy with Elias because I think he was quite dangerous - more than once he passed me on the inside and then altered his line. This is not a correct way to race," he said.

Stoner said: "I got past Colin Edwards quickly on the first lap and then Valentino Rossi when he went too wide on a corner.

"Then once in front I just went into a mental blockout for the next two laps and that enabled me to stay focused."

Italian Simon Corsi clinched victory in the 125cc race but there were good performances from the Brits.

Bradley Smith finished eighth after a bump with another rider on the last lap saw him drop back from sixth.

Scottish teenager Kev Coughlan was an impressive 21st in only his second GP appearance and Danny Webb was 23rd.

Results from Turkish MotoGP, Istanbul:

1. Casey Stoner (Aus) Ducati 42 minutes 2.85 seconds
2. Toni Elias (Spa) Honda 42:09.057
3. Loris Capirossi (Ita) Ducati 42:10.952
4. Alex Barros (Bzl) Ducati 42:10.985
5. Marco Melandri (Ita) Honda 42:11.139
6. John Hopkins (US) Suzuki 42:13.036
7. Nicky Hayden (US) Honda 42:13.089
8. Randy de Puniet (Fra) Kawasaki 42:17.584
9. Alex Hofmann (Ger) Ducati 42:18.892
10. Valentino Rossi (Ita) Yamaha 42:21.849

Overall points standings:

1. Casey Stoner (Aus) Ducati 61
2. Valentino Rossi (Ita) Yamaha 51
3. Dani Pedrosa (Spa) Honda 36
4. Toni Elias (Spa) Honda 35
5. Marco Melandri (Ita) Honda 30
6. Colin Edwards (US) Yamaha 26
7. Nicky Hayden (US) Honda 26
8. Alex Barros (Bzl) Ducati 25
9. John Hopkins (US) Suzuki 23
10. Chris Vermeulen (Aus) Suzuki 21

250cc class selected results:

1. Andrea Dovizioso (Ita) Honda 39:31.153
2. Jorge Lorenzo (Spa) Aprilia 39:31.256
3. Alvaro Bautista (Spa) Aprilia 39:31.471

17. E Laverty (Irl) 41:20.981

125cc class selected results:

1. Simone Corsi (Ita) Aprilia 40:03.557
2. Joan Olive (Spa) Aprilia 40:03.655
3. Tomoyoshi Koyama (Jpn) KTM 40:05.500