Jorge Lorenzo held his hands up to having been at fault for his crash at the Japanese MotoGP, which helped Marc Marquez take his world title crown.
Lorenzo and Yamaha team-mate Valentino Rossi failed to finish in Motegi, meaning Marquez built an unassailable lead in the standings to secure his third championship in four years.
But the title race could still have been alive heading to Australia next week had Lorenzo - who suffered a painful crash in Saturday's qualifying - not made an error when trying to stay ahead of Andrea Dovizioso with only five laps remaining.
"I'm very disappointed, because I made a mistake," said the Spaniard, who also lamented his tyre choice. "I tried to push too much when the bike was not working well with the tyres.
"In Aragon we made a good decision with the tyres and this time it was the opposite. We chose the wrong front tyre, with the soft I think I would have made a better race, because my front tyre on the first laps was vibrating and closing.
"I didn't have a good feeling, that's why I couldn't keep up with the pace of Marquez.
"Finally, because Dovizioso was coming, I pushed more than before in that corner and the front tyre didn't give me any support or feedback and I crashed.
"It's a pity because here we had a great chance to win. The crash [on Saturday] made the race more difficult because of the pain and also with the mistake on the front tyre. So we lost a great opportunity to win."