Francesco Bagnaia survived a late scare to finish second in the Qatar MotoGP as his only title rival Jorge Martin limped home 10th complaining he had been given a bad tyre.
Fabio Di Giannantonio, who does not have a ride next season took his first victory and, he said, "revenge" on "everybody who doubted me."
Luca Marini was third on a VR46 Ducati.
Defending champion Bagnaia leads Martin by 21 points with one weekend left in Valencia where the maximum haul for a rider who wins both the sprint and the main race is 37 points.
Martin had cut Bagnaia's lead to seven points by winning the sprint the day before. But in the main race, the Spaniard slipped to ninth after a bad start and struggled throughout on his Ducati Pramac, eventually coming home 10th.
"I had a really bad rear tyre," the Spaniard said. "You could see already see at the start when you start to spin and you are the only one."
"I think it's a pity that the championship is decided by a bad tyre," he said. "We are in MotoGP and this is unacceptable. I had the potential to win the race. I feel like they beat me outside the track not on the track."
Bagnaia had no such problems, sweeping into the lead from the start on his Ducati with only fellow Italian Di Giannantonio able to keep up.
"I was alone in the front. I tried to push but Digia today was incredible," said Bagnaia.
Di Giannantonio bided his time behind Bagnaia saying he was aware that his rival was chasing the title and did not want to take him out.
"I'm sorry for him if I stole five points from him," said Di Giannantonio. "I tried to be as smooth as possible but I was trying to win my first race. I think my pass was worth it."
Bagnaia was prepared to take the risk.
"I wanted to win today. It was the only
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