Julian Simon has extended his lead at the top of the 125cc World Championship with his fourth victory of the season after race leaders Andrea Iannone and Pol Espargaro crashed out at the final turn.
Espargaro, who took his first victory last Sunday at Indianapolis, had made a brilliant comeback to snatch the lead from home hero Iannone with three laps to go.
The last lap began with Espargaro, Iannone and Simon in close formation, with Espargaro keeping his Derbi defensive to leave Iannone without a chance to pass.
But heading into the final turn, Iannone dived for the inside of Espargaro, but lost the front wheel of his Ongetta Aprilia - taking them both out. As Simon cruised to victory, Espargaro's bike was sent cart-wheeling over a tyre barrier, before the distraught young Spaniard confronted Iannone.
Some pushing and shoving followed before Iannone head-butted Espargaro, a move that had little effect given both were wearing crash helmets, but a gesture which he could well come to regret once Race Direction have examined the footage.
The last turn drama promoted early leader Nicolas Terol (Jack & Jones Aprilia) to second and Simon's Aspar Aprilia team-mate Bradley Smith to third.
Simon, who began round twelve 52.5 points ahead of Terol, is now 57.5 points clear, with Smith five points further back with four rounds to go.
Aprilia has now wrapped up the 2009 constructors' championship.
Race results - Misano:
1. Simon (Aprilia)
2. Terol (Aprilia) +0.573sec
3. Smith (Aprilia) +5.474sec
4. Marquez (KTM) +9.378sec
5. Cortese (Derbi) +9.665sec
6. Bradl (Aprilia) +11.755sec
7. Corsi (Aprilia) +23.044sec
8. Olive (Derbi) +26.936sec
9. Folger (Aprilia) +32.851sec
10. Webb (Aprilia) +34.439sec
Redding (Aprilia) DNF