Alex Marquez, brother of MotoGP world champion Marc, extended his Moto3 lead over Jack Miller to 25 points with three races to go after a dramatic last lap at Motegi.
Marquez and 2015 LCR MotoGP signing Miller were part of a six-bike lead battle throughout the series' Japanese Grand Prix, and it initially seemed that Miller would be able to reduce the advantage his rival established after their Aragon collision.
While Miller led much of the distance, Marquez got involved in several tight moments with the Australian's Ajo stablemate Danny Kent, who had started from pole.
Kent got between the title rivals going onto the last lap, but then challenged Miller for the lead onto the long back straight.
As the leading trio went three-abreast, both Kent and Miller outbraked themselves into Turn 11 and ran wide, allowing Marquez to sweep through while the Ajo pair banged into each other on the kerbs.
Marquez duly collected his third win of the year, with Miller and Kent rejoining fifth and sixth behind Efren Vazquez, Brad Binder and John McPhee.
The title fight is now effectively a two-horse race, as Marquez's Monlau team-mate Alex Rins - third in the standings - fell 37 points adrift after finishing only 10th, having fallen to 21st when he ran wide at the first corner.
Romano Fenati, lead rider for Valentino Rossi's VR46 team, was unable to capitalise on his win last time out at Aragon and finished seventh, leaving him 57 points behind with only 75 available.
CHAMPIONSHIP STANDINGS AFTER 15 OF 18 ROUNDS: