Ducati's defending world champion Francesco Bagnaia has won the MotoGP season-opening Qatar Grand Prix after taking the lead on the opening lap to beat Red Bull KTM's Brad Binder and Pramac Racing's pole sitter Jorge Martin.

But it proved a bad day for Jack Miller, as the Australian had top bail off the track at the opening turn and rejoin the race in last place, from which he never recovered, eventually coming home at the rear of the field in 21st place on his Red Bull KTM.

Bagnaia had finished fourth in Saturday's sprint but his faultless ride to take the chequered flag in the main race 24 hours later moved him to the top of the championship with 31 points.

Binder, who also finished second in the sprint, sits two points behind with 29 while last year's championship runner-up Martin is a point further behind.

"We tried to do the maximum knowing something important had to be changed for today's race. After today's warm-up (the bike) was absolutely different to yesterday," Bagnaia said after his first victory at the Lusail International Circuit.

Marc Marquez finished fourth on his Gresini Racing debut aboard a Ducati bike following his switch from Honda while 19-year-old rookie Pedro Acosta nearly stole the show in search of a podium before falling back to finish ninth.

Martin and Binder both shot off the line at the start as they did in Saturday's sprint to sit first and second, but Bagnaia put his head down and made two daring overtakes to take the lead on the opening lap.

"I'm super stoked with the result today. We knew it was going to be tough to make the tyres last until the end," said Binder, who finished 1.3 seconds behind Bagnaia.

Martin had dominated qualifying and the sprint but he soon found himself in a battle for second with Binder while Gresini's Alex Marquez moved up to fifth to sit behind his brother Marc.

Behind him, Acosta set a fastest lap and the Red Bull GasGas Tech3 rider rode fearlessly to quickly move up to sixth before the 19-year-old rookie soon overtook both the Marquez brothers to sit behind Martin.

But as the race wore on, Acosta looked like he was struggling for grip and the experienced Marc - who had been conserving his tyres - took advantage to move up to fourth when the rookie went wide.

Earlier, the race was reduced to 21 laps after Raul Fernandez had an issue with his Trackhouse Racing bike just before the lights went out and the start was delayed after he refused to move it into the pit lane.

After technicians failed to get his machine going, Fernandez was forced to sprint back to their garage to hop on a spare bike and start the race from the pit lane, but he was eventually forced to retire from the race - the only rider not to finish.