Casey Stoner took advantage of a crash by MotoGP championship leader Jorge Lorenzo to blow the title race wide open with victory at Assen.
Lorenzo saw his 25-point lead disappear when he was recklessly taken out at the first corner by Alvaro Bautista.
Stoner held off Repsol Honda team-mate Dani Pedrosa to win and move level on points with Yamaha rider Lorenzo.
British rider Cal Crutchlow was also hampered by Bautista's crash but recovered to finish in fifth place.
Crutchlow's team-mate Andrea Dovizioso took third place after passing Ben Spies on the final lap.
After Pedrosa made his trademark fast start to lead into turn one Lorenzo's race was finished by Bautista, handing the initiative back to Stoner in the race for the title.
Lorenzo had no chance of avoiding a crazy move up the inside from Gresini Honda rider Bautista, who lost control and sent both himself and the Spaniard into the gravel trap.
Crutchlow - racing two weeks after breaking his ankle at Silverstone - was also forced off the track by Bautista's accident and found himself back in 15th place.
However, for the second race in a row the Briton worked his way through the field to eventually take a very creditable fifth spot.
Stoner was able to pass Pedrosa in the closing stages and pull away to claim 25 vital points.
Stoner told BBC Sport: "I didn't see that Lorenzo had crashed as I was focused on the fight at the front but what a difference a day makes.
"I had a big crash in practice on Friday but we managed to pull through for the race. Today has worked out perfectly for me.
"I'm sorry for Jorge, nobody wants to take points over a competitor in this manner, but as we can see, one race can change everything."
Championship leader Marc Marquez strengthened his lead at the top of the Moto2 standings with a fine win.
Marquez held off Andrea Iannone to win for the third time this season while title challengers Thomas Luthi and Pol Espargaro both crashed out in the opening laps.
British rider Scott Redding was able to finish third for his second podium in a row.
Marquez - who is set to move into MotoGP next season - now holds a 23-point lead over Iannone in the standings.
In the day's earlier Moto3 race, British rider Danny Kent held the lead for much of a sensational race but was nearly knocked off by an aggressive move from team-mate Sandro Cortese.
Maverick Vinales eventually pulled out an overtaking move at the last corner to win and extend his championship lead over second-placed Cortese, with Kent claiming his first podium finish in third after a photo-finish.
Stoner tweeted: "Cortese needs to have more than a slap on the wrist for his riding in this Moto3 race. He's going to cause a huge crash if he doesn't stop it."
Assen MotoGP results:
1. Casey Stoner (Aus) Repsol Honda 41:19.855
2. Dani Pedrosa (Spa) Repsol Honda 41:24.820
3. Andrea Dovizioso (Ita) Tech 3 Yamaha 41:31.849
4. Ben Spies (USA) Yamaha 41:34.630
5. Cal Crutchlow (GB) Tech 3 Yamaha 41:41.929
6. Nicky Hayden (USA) Ducati 41:51.515
7. Hector Barbera (Spn) Pramac Ducati 42:18.962
8. Randy de Puniet (Fra) Aspar ART 42:24.296
9. Michele Pirro (Ita) Gresini FTR 42:26.835
10. Mattia Pasini (Ita) Speed Master ART 42:44.942