Melandri overtook Stoner to win in Turkey for the second straight year

Melandri, who started 14th, first took the lead on lap 11, and he Dani Pedrosa, Nicky Hayden and Stoner battled for the rest of the race.

Stoner, who won last year's 250cc race, hit the front with four laps to go only for Melandri to make his decisive move.

American Nicky Hayden was third, with world champion Valentino Rossi fourth.

Rossi, in his 100th top-class race, inherited the position when Pedrosa crashed out of fourth place on the last lap.

Hayden is the new championship leader by one point, taking over from Italy's Loris Capirossi who finished sixth.

Surprise pole sitter Chris Vermeulen had to settle for seventh after failing to hold off his charging rivals early on in the 22-lap race.

To be leading the world championship is an accomplishment and I'm proud of it Nicky Hayden

Melandri was delighted as his victory from 14th on the grid after a wet qualifying session on Saturday, maintained Italy's winning streak with the country's riders taking the last 12 races.

"It was like the 125s," he grinned after a race that saw the top three and Pedrosa jostling for the lead.

Hayden's seventh successive podium finish was still not the top step he was looking for but the championship lead was a consolation.

"We had a few little issues," said the American, revealing that the tyre warmer had melted to a front brake disc on the grid.

"I don't want to sound like I'm making a lot of excuses, but nonetheless I'm pretty lucky to escape with what I got.

"Bottom line, I didn't get it done today. It was exciting, everybody riding super-aggressive but nobody really doing any bone-head moves," said Hayden."

"To be leading the world championship is an accomplishment and I'm proud of it."