Quartararo repeated his route to victory in Doha, Algarve, recovering from sixth place at the end of the first round to take an early lead and dominate to gain a 15-point lead in the championship.
Johann Zacro put his Pramac Ducati in the lead early on when policeman Quartararo fell back while Marquez jumped to third place.
Marquez was then downgraded by reigning world champion Joan Mir, the Suzuki rider who made an aggressive move on the Honda at the Portimao right-handed man.
The pair hit again at Turn 3 on the following lap when Marquez touched the rear of Mirs Suzuki and was fortunate enough to remain mounted. Quartararo used it to move back up to fourth place.
In the lead battle, Zarco held on, but came under heavy pressure from sister Rins’ Suzuki, who made a pass stick on lap 13 at turn 13 – although Zarco came back up the main straight a moment later.
Rins played another game for the lead at the end of lap five at turn 13, while Quartararo slipped through to Zarco at the next turn.
The Suzuki rider took the lead for the next two laps, and Quartararo dragged himself into Turn 1 on the ninth tour through Rins.
The pace for Quartararo and Rins was hot. The couple drove the fastest laps several times and was able to close a gap of more than a second compared to the fighting Zarco and Mir behind them.
Rins kept the pressure on Quartararo but the Frenchman didn’t crack and kept his lead.
Race winner Fabio Quartararo, Yamaha Factory Racing
Photo by: Gold and Goose / Motorsport Images
Quartararo’s afternoon was relieved with seven laps to go when Rins pushed too hard in his chase and retired at Turn 5, giving the Yamaha rider well over four seconds ahead of the remaining tours.
Rins’ fall put Zarco in second place while Ducati’s Francesco Bagnaia found a way through Mir.
However, Zarco’s podium was finished on lap 20 when he crashed at Turn 10. The battle for second place was between Bagnaia, Mir and Franco Morbidelli from Petronas SRT.
Quartararo was not threatened by the checkered flag to secure his second straight win in 2021.
Bagnaia struggled against Mir and took second place with his Ducati, while Morbidelli was fourth from 15th on the grid, ahead of Brad Binder of KTM.
Aleix Espargarao was a factor in the podium early on, but the Aprilia rider finished sixth and got his best result at the RS-GP.
Marc Marquez’s last MotoGP race before Sunday’s Portuguese GP ended in a potentially career-threatening crash.
Marc Marquez, Repsol Honda Team
Photo by: Gold and Goose / Motorsport Images
But he put those demons in seventh place in the Algarve, the six-time MotoGP world champion who led home his LCR Honda-mounted brother Alex Marquez, Avintia rookie Enea Bastianini and injured Takaaki Nakagami (LCR).
Maverick Vinales suffered a mysterious loss of form at the end of the first lap on his Yamaha, the Qatar GP winner, and was only able to save 11th place after a series of falls.
He ran Luca Marini (Avintia), Danilo Petrucci from Tech3, Lorenzo Savadori from Aprilia and the Tech3 sister bike from Iker Lecuona, while last year’s Portuguese race winner Miguel Oliveira finished 16th after a crash.
Valentino Rossi crashed from eleventh in the closing stages and the SRT rider joined Ducati’s Jack Miller after an early crash.
Pol Espargaro retired at the end of lap five due to a technical problem with his Honda.
Result – 25 rounds