Suzuki's Alex Rins came in second after overtaking Yamaha rider Johann Zarco, who finished third, in the final stage of a hard-fought race at Sepang in baking hot temperatures.

Italian star Rossi, a nine-time world champion who has struggled recently to find form against younger foes, appeared on course for his first win in Malaysia since 2010 after a strong start from second on the grid put him firmly in the lead.

But Honda's Marquez, who won the world title last month for the fifth time in motorcycling's premier class, methodically fought his way up through the pack after beginning near the back.

The Spaniard, who qualified in pole position but was hit with a six-place grid penalty for impeding another rider, made it to second place and was starting to close the gap on Rossi, 39.

It looked like the final stage of the Malaysian Grand Prix would be a classic battle between two MotoGP titans known for their fierce rivalry. But as he rounded a sharp turn on the 16th lap, Yamaha rider Rossi leaned over too far and tumbled off his bike -- effectively handing victory to his 25-year-old foe.

Rossi, who has won in the premier class at Sepang on five previous occasions, got back on his bike but only managed to finish a lacklustre 18th.

"It is a great, great shame, I am very disappointed for the mistake," admitted a crestfallen Rossi, who has not won a race this season. "It is frustrating."

But he tried to look on the bright side: "It is the best race of the season for me, it is also coming in a difficult condition and a difficult track for us. This is important."

Marquez cruised to a comfortable victory in 40 min 32.372 sec, with Rins and Zarco left far behind battling it out for second place.

Marquez, who notched up his ninth win of the season Sunday and his first in Malaysia since 2014, said that fighting his way up from the back was not easy. "It was a very, very, very hard race," he said, but added that having the odds stacked against with a third row start proved to be an "extra motivation".

It is not the first time this season that Marquez has lost his pole position due to a penalty, and nevertheless gone on to victory.

At the Grand Prix of the Americas in April, he was demoted from first to fourth on the starting grid after being punished for disturbing another rider in qualifying. He went on to win that race for the sixth consecutive time.

Ducati's Andrea Dovizioso, the winner in Malaysia in 2016 and 2017, could only manage sixth but retains second place in the overall standings, with Rossi's crash leaving the Italian in third with one race remaining.

Conditions were dry after organisers shifted the MotoGP two hours earlier following a delay to Saturday's qualifying session caused by a tropical downpour.

However many riders struggled in the soaring temperatures.

The 2016 and 2017 editions of the MotoGP took place during heavy downpours. In the Moto2 class, Italy's Francesco Bagnaia won the world title while Jorge Martin from Spain was crowned world champion in the Moto3 category.