Antonio Felix da Costa also jumped Muller during the stops, but he could not get on terms with the leaders and had to turn his focus to keeping the Monaco race winner at bay.
The top five were well clear of the rest of the field, where Carlos Sainz Jr and Nigel Melker - who had a rather embarrassing clash with Tech 1 team-mate Mikhail Aleshin earlier in the race - fought hard for sixth.
Their scrap brought Jazeman Jaafar into the equation, and shortly after Melker found a way into sixth, Sainz and Jaafar collided at Malmedy on the penultimate lap, putting both out.
Results - 21 laps:Pos Driver Team Time/Gap 1. Stoffel Vandoorne Fortec 47m06.630s 2. Will Stevens P1/Strakka + 4.536s 3. Kevin Magnussen DAMS + 6.203s 4. Antonio Felix da Costa Arden Caterham + 7.138s 5. Nico Muller Draco + 8.490s 6. Nigel Melker Tech 1 + 19.702s 7. Nikolay Martsenko Pons + 26.531s 8. Sergey Sirotkin ISR + 27.406s 9. Oliver Webb Fortec + 28.133s 10. Marco Sorensen Lotus + 29.203s 11. Matias Laine P1/Strakka + 31.278s 12. Pietro Fantin Arden Caterham + 32.463s 13. Christopher Zanella ISR + 33.444s 14. Mihai Marinescu Zeta + 42.661s 15. Norman Nato DAMS + 44.280s 16. Zoel Amberg Pons + 46.298s 17. Marlon Stockinger Lotus + 46.617s Retirements: Carlos Sainz Jr Zeta 19 laps Jazeman Jaafar Carlin 19 laps Carlos Huertas Carlin 17 laps Mikhail Aleshin Tech 1 6 laps Daniil Move SMP/Comtec 0 laps Yann Cunha AV 0 laps Andre Negrao Draco 0 laps Arthur Pic AV 0 laps Lucas Foresti SMP/Comtec 0 laps
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