Johann Zarco finished 11th for JIR, while Tito Rabat made up an incredible 15 places to finish 12th for the Pons 40 HP Tuenti team.
Former 125cc champions Nico Terol (Mapfre Aspar) and Julian Simon (Blusens Avintia) finished 14th and 15th respectively.
Iannone made up ground in the opening laps aboard his Speed Master to challenge Marquez at the front, overtaking him with 22 laps to go.
He had to push hard to stick with the Spaniard, which eventually resulted in a crash for Iannone a couple of laps later, he rejoined to finish 16th and out of the points.
Scott Redding crashed out on the first lap when Toni Elias sitting up on his bike forced the Marc VDS rider down and into the gravel. Elias later crashed out himself.
Gino Rea did his best to hold his ground aboard his Federal Oil Gresini(Suter) but couldn't translate his best qualifying from fifth into something special and finished a hard fought 18th
The Moto2 championship continues next weekend when the racing heads to Mugello, Italy.