Last year's Italian 125cc runner-up Fenati blasted into the lead from sixth on the grid at the start, while pre-season title favourite Vinales dropped back to fourth. The Spaniard - hotly-tipped for 2012 after winning four 125cc races in his rookie season at world level in '11 - soon fought through to join Fenati at the front, as they broke away from the rest of the field.
Vinales (Avintia) bided his time behind Fenati (Italia FMI) until lap six, when he swept past into Turn 1. He could not shake Fenati off at first, and would have to relinquish the lead again as the young Italian retaliated on lap 10.
But Vinales drafted back ahead two laps later, and after that started to storm away, eventually beating Fenati to victory by 4.3 seconds.
A massive battle for third showed that Moto3 will produce racing just as spectacular as its 125cc predecessor had. Polesitter Sandro Cortese eventually grabbed the final podium spot for the Ajo team, but only after an epic side by side pack race with Luis Salom (RW), Miguel Oliveira (Monlau), Ajo trio Zulfahmi Khairuddin, Arthur Sissis and Denny Kent, and Team Germany's Louis Rossi.
Monlau's highly-regarded Spanish newcomer Alex Rins beat fellow world-level rookie Alan Techer (Technomag-CIP) and veteran Aspar rider Hector Faubel to 10th.