Alex Marquez, who confirmed his runner-up spot in the world championship this weekend behind brother Marc, won for the first time this year outside Spain following success at the Spanish and Catalan Grand Prix races.

Honda's Joan Mir was third to make it an all-Spanish podium, with Franco Morbidelli and Fabio Quartararo completing the top five.

Newly crowned world champion Marc Marquez was absent because of a season-ending injury.

Alex Marquez called it the "perfect race".

"It's a really important win for us to celebrate second (in the championship)," said the younger Marquez, 29.

Pole-sitter Francesco Bagnaia, who won Saturday's sprint, started well on a hot and humid Sepang circuit to hold a slender lead in the first lap with Acosta and Marquez in hot pursuit.

Marquez, who started second on the grid, made his move early in the second lap as the Ducati-Gresini star surged past Bagnaia during a sweeping corner, and maintained the lead until the finish line.

"Today the plan was clear," said Marquez.

"We improved the feeling a bit on the warm-up and later on I was clever on the plan to attack Pedro in the first lap and Pecco (Bagnaia) in the second one.

"Then I just tried to manage the tyre towards the end. It was a perfect race and I'm happy for that."

Ducati's Bagnaia had a tailgating Acosta behind him as the front three left the chasing pack behind.

As the race reached the halfway stage, Bagnaia's focus was to fend off intense pressure from Acosta, leaving Marquez to increase his advantage.

Acosta's pressure eventually paid off as the KTM rider found joy on the 13th lap to overtake Bagnaia into second place.

Unperturbed by the battle unfolding behind him, Marquez crossed the finish line in 40 min 09.249 sec.

Bagnaia's afternoon ended with a bike issue late on that left him unable to finish the race.

- 'Prayers' after crash -

Earlier, the Moto3 race was delayed and shortened after a nasty collision involving newly crowned world champion Jose Antonio Rueda and Noah Dettwiler during the sighting lap.

Both riders were airlifted to hospital but were conscious.

"My prayers and thoughts are with the Moto3 guys," said Marquez.

MotoGP organisers subsequently gave an update on social media about the 19-year-old Spaniard Rueda.

It said: "Rueda is awake and alert, with a suspected hand fracture and a number of contusions."

There was no immediate news on the condition of Switzerland's Dettwiler.