Alex Marquez, brother of MotoGP world champion Marc, moved into the Moto3 championship lead after a controversial tangle with rival Jack Miller at Aragon.
The younger Marquez had closed to within nine points of season-long leader Miller - who will move straight into MotoGP with LCR Honda next year - heading into this weekend's race.
They then came together while battling for the race lead in the early stages of the Aragon race, which took place on a track still drying after earlier rain.
Miller was attempting to hang on around the outside of Marquez at the end of the Spanish venue's back straight when the two riders drifted into each other.
While Marquez stayed on his bike, Miller was pitched into the air.
He was able to recover to the pits, where the Ajo team repaired his KTM so he could rejoin three laps down, finishing 27th after another fall late on.
The collision is being investigated by MotoGP race direction, although under the series' penalty system, any punishment is more likely to take the form of points on a rider's licence rather than a result alteration.
Marquez was ultimately denied the race victory by 0.057 seconds by the resurgent Romano Fenati, who rides for Valentino Rossi's VR46 team. The Italian dropped out of contention with a run of poor races in the summer, and had not won since Mugello in June.
Despite the defeat, second place for Marquez still moved him into an 11-point lead over Miller with four rounds remaining.
Marquez's Monlau team-mate Alex Rins has closed to within seven points of Miller in third after finishing fourth at Aragon following a mid-race mistake when challenging Marquez for the lead.