Francesco Bagnaia clinched victory in the rain-soaked Thai MotoGP on Sunday, narrowing the points gap behind championship leader Jorge Martin with just two race weekends remaining.

Spaniard Martin's lead over Italian defending champion Bagnaia was cut from 22 points to 17 ahead of another chapter in their title tussle at Sepang in Malaysia next week.

Pedro Acosta was third at a rainy Buriram but this was all about Martin and Bagnaia, with the title now a two-horse race and likely to go right down to the wire.

After Malaysia, the season finale is at Valencia on Nov. 15-17.

Pramac Ducati's Martin, who is trying to win the world crown for the first time, said he was happy to settle for second, coming home nearly three seconds behind.

"The level we are demonstrating – not a lot of people can understand how fast we are going even in these conditions," he said.

Bagnaia thanked his Ducati team for keeping his hopes of a third world title in a row alive.

The 27-year-old said he had never won in the rain before.

"It was a day to make the difference and luckily we did it," he said.

"Wasn't an easy race, it was very long and stressful but as soon as I started my feeling was good.

"I knew it was important to make up points in the championship.

"It's a good day for us and 17 (gap in points) is a good number for me."

Martin feeling the heat

Martin began the race on the front row in third and made a lightning start to grab the lead from his pole-sitting rival.

But the 26-year-old did not stay there long, running wide to fall to third as Bagnaia took the lead with six-time MotoGP world champion Marc Marquez in hot pursuit.

It had developed into a duel between Bagnaia and Marquez at the halfway point of the 26-lap race, with Martin struggling to keep up.

But Marquez pushed too hard in trying to take the lead and slid off on his Ducati.

That left the title rivals to battle it out for victory, but Bagnaia held his nerve and handled the demanding conditions to see out a crucial ninth win of the campaign.

"Was a really challenging race today," said Martin, who had a couple of hairy moments but is still in the driving seat for the world crown.

"I don't want anybody to feel what I felt before the race," he said of the pressure to keep Bagnaia at bay, admitting he "felt the tension six or seven races ago."

"Being me and Pecco (Bagnaia) at this stage of the championship, with these conditions, is not good."

Bagnaia also started Saturday's sprint race on pole but ended up third, just behind Martin. Bagnaia's Ducati teammate Enea Bastianini won the sprint.

Earlier, Japan's Ai Ogura was crowned Moto2 world champion as he came second in a red-flagged race won by Spain's Aron Canet.

The 23-year-old Ogura will move up to MotoGP next season.