Honda’s Marquez made seven attempts to overtake Bagnaia in the last three laps but failed to make a move and the Ducati rider prevailed to become the eighth winner of 2021.
Bagnaia maintained pole position outside the line, while Marquez passed Jack Miller in the first corner and moved from fourth on the grid to second.
A dubious start for championship leader Quartararo dropped him to fifth place, and the Yamaha rider would lack the urge to move forward on the following laps.
On lap six, Quartararo was relegated to seventh place by Pramacs Jorge Martin and Tech3 KTM rider Iker Lecuona, and Brad Binder’s factory KTM soon found a way past Quartararo to demote Quartararo to ninth place.
At the front, Bagnaia and Marquez ran a strong pace and were quickly over six tenths between themselves and Miller in third place.
And that gap grew bigger and bigger as the race progressed as both Bagnaia and Marquez drove practically identical laps in a tense battle for victory.
Miller’s hopes for the podium vanished at the end of lap 11 when he went off track on the last two corners and let Aprilia’s Aleix Espargaro and Joan Mir’s Suzuki prevail.
I then moved to the left at Turn 4 to third place in front of Espargaro.
Start action
Photo by: Gold and Goose / Motorsport Images
As the race continued, the gap that Bagnaia and Marquez built on the field behind increased to over four seconds, 10 of the 23 remaining laps.
A sharp drop in lap times for the field – all on soft back rubber – was expected around lap 15, but the pace of Bagnaia and Marquez remained consistent and strong.
On lap 21, Marquez made his first of seven attempts to take the lead from Bagnaia, this time at Turn 5.
But the Honda rider was able to hold the line through the exit and Bagnaia came right back through – exactly the same at Turn 15 later on the lap.
On the following tour, Marquez repeated his attempts at the same two corners, but was again pushed off by the Ducati rider.
On the last lap, Marquez tried to overtake Bagnaia in the first corner, but ran too far and was blocked again in turn 5.
Marquez threw one last try against Bagnaia at Turn 12 on the left but ran in too hot and left Bagnaia to take the checkered flag 0.673 seconds ahead of the Italian to celebrate Ducati’s first Aragon win since Casey Stoner in 2010.
Reigning world champion Mir completed the podium after Aleix Espargaro lost the pace late in fourth, while Miller completed the top 5.
Joan Mir, Team Suzuki MotoGP
Photo by: Gold and Goose / Motorsport Images
Avintia rookie Enea Bastianini made it to the best sixth place of the season on his two-year-old Ducati and overtook Binder late.
On Saturday, Quartararo admitted that he didn’t feel he had the pace for the podium and barely held eighth place, 0.040 seconds ahead of Martin.
With Bagnaia’s victory, Quartararo’s championship lead has now been reduced from 65 to 53 points on the way to Misano.
Takaaki Nakagami completed the top 10 on the only LCR Honda at the finish after teammate Alex Marquez crashed on lap, while Lecuona dropped to 11th after a late mistake.
Alex Rins recovered from 20th to 12th place on the second Suzuki, Hondas Pol Espargaro, Miguel Oliveira on the factory KTM and Tech3s Danilo Petrucci secured the last points.
Yamaha deputy Cal Crutchlow finished 16th in what is expected to be his last race in 2021, while Johann Zarco on his Pramac Ducati finished 17th.
Maverick Vinales finished his first race as Aprilia rider 18th and 27.1 seconds behind the win ahead of Valentino Rossi of Petronas SRT and Luca Marini of Avintia.
SRT deputy Jake Dixon crashed in the second round.