Fabio Quartararo held off Francesco Bagnaia to take Moto2 victory in the Japanese Grand Prix, but was later disqualified from the result due to a tyre pressure infringement, handing the win to Bagnaia.
Quartararo took the lead from fellow MotoGP-bound rookie Bagnaia early on, and kept the Italian at bay to beat him by 0.445 seconds for his second win of the year before being stripped of the result after his rear tyre was found to have been under the advised limit set by Dunlop.
Quartararo seized the lead from Bagnaia on the run into the first corner at the start, but ran wide and was picked off by the Sky VR46 rider at Turn 2.
By the end of the opening lap, Bagnaia and Quartararo had already opened up a lead of half a second over Pons' Lorenzo Baldassarri, while Bagnaia's title rival Miguel Oliveira made little progress from ninth on the grid on his Ajo KTM.
Quartararo lined up a move on Bagnaia into Turn 11 on the third lap, and held the inside line into the next corner to secure the position before putting half a second between his Speed Up and the VR46 Kalex.
The leading duo continued to extend their advantage over the chasing Baldassarri as the race went on, with the gap between Quartararo and Bagnaia fluctuating as the pair responded to each other's charges.
Bagnaia made his first play to regain the lead he lost early on with a daring move at Turn 7 with four laps remaining, but was not far enough alongside the Frenchman to trouble him.
Quartararo led across the line at the start of the final lap, and resisted pressure from Bagnaia to claim what should have his first win since his debut victory in Barcelona.
Baldassarri completed the podium in a lonely third, though is now promoted to second ahead of KTM's Oliveira thanks to Quartararo's sanction. Bagnaia now leads the points by 37.
Alex Marquez battled through injury from a heavy fall in FP2 to finish as lead Marc VDS rider in fifth ahead of the sister Ajo KTM of Brad Binder.
Augusto Fernandez was seventh on the second of the Pons bikes, while Vierge [IntactGP] faded to eighth late on ahead of front row starter Iker Lecuona [CGBM Evolution] and Bagnaia's teammate Luca Marini.
The final points went to Marcel Schrotter on the second Intact bike, Marquez's stablemate Joan Mir, home favourite Tetsuta Nagashime [Honda Team Asia], Kiefer's Dominique Aegerter and Mattia Pasini [Italtrans].
Tasca Racing duo Simone Corsi and Federico Fuligini crashed out of the 22-lap race, as did Gresini's Jorge Navarro and Tech3 rider Bo Bendsneyder.
