The McLaren junior converted pole position into the lead at the start thanks to some strong defending against fellow front row starter Sergey Sirotkin, and he was never challenged after that.
As Magnussen pulled away to open out what would be a 19-second lead by the finish, Arthur Pic spent most of the race in second after swooping around the outside at the start.
However, the Frenchman was reeled in by a charging Will Stevens in the closing stages, and after a couple of errors from Pic late in the race Stevens was able to take second - having started 11th - on the exit of Turn 1 on the final lap.
Sirotkin fought off the advances of Magnussen's DAMS team-mate Norman Nato to take fourth. Before the pair were passed by Stevens, Nato had made one failed attempt at taking the place, but Sirotkin was able to keep him under control after that.
Nigel Melker and Christopher Zanella were next up, the latter holding off former championship leader Stoffel Vandoorne and Marco Sorensen to the flag.
Sorensen had run fifth in the early laps, but he and Vandoorne both lost places at the end of the seventh lap, which left them stuck towards the bottom of the points for the rest of the race.
For the second event running Vandoorne had to nurse a badly flat-spotted tyre to the finish, after he suffered a big lock-up at the end of the opening lap.
Red Bull junior Antonio Felix da Costa, who was sent to the back of the grid after his car ran out of fuel in qualifying, recovered to 13th place and missed out on the points by a little over five seconds.
The Arden Caterham driver climbed from 26th to 18th in the first few corners, but from there his progress was slow as he battled in the middle of the pack.
Magnussen's win gives him the lead in the championship, 17 points clear of Vandoorne.
Results - 27 laps: Pos Driver Team Time/Gap 1. Kevin Magnussen DAMS 46m15.323s 2. Will Stevens P1 + 19.933s 3. Arthur Pic AV Formula + 21.266s 4. Sergey Sirotkin ISR + 23.601s 5. Norman Nato DAMS + 24.398s 6. Nigel Melker Tech 1 + 26.094s 7. Christopher Zanella ISR + 34.943s 8. Stoffel Vandoorne Fortec + 35.419s 9. Marco Sorensen Lotus + 36.065s 10. Mikhail Aleshin Tech 1 + 37.973s 11. Oliver Webb Fortec + 41.520s 12. Nikolay Martsenko Pons + 42.016s 13. Antonio Felix da Costa Arden Caterham + 42.609s 14. Lucas Foresti Comtec + 1m04.474s 15. Yann Cunha AV Formula + 1m15.586s 16. Matias Laine P1 + 1m17.124s 17. Zoel Amberg Pons + 1m18.185s 18. Jazeman Jaafar Carlin + 1m18.934s 19. Marlon Stockinger Lotus + 1m23.597s 20. Carlos Huertas Carlin + 1m25.368s 21. Daniil Move Comtec + 1m31.909s 22. Matheo Tuscher Zeta Corse + 1m45.147s Retirements: Andre Negrao Draco 23 laps Pietro Fantin Arden Caterham 20 laps Mihai Marinescu Zeta Corse 17 laps Nico Muller Draco 0 laps
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