Magnussen's effort demoted Alexander Rossi to second, after the American had taken top spot from title contender Sam Bird 10 minutes earlier.
A late improvement from Nick Yelloly completed a good day for the Briton. The Comtec driver had led the way in the morning session, which took place in sunnier conditions than the afternoon running.
Yelloly's time dropped championship leader Robin Frijns to fourth. The Dutchman did at least get ahead of title rival Bird near the end, but he had to return to the pits with the help of a tow-truck after stopping at Turn 2 in the closing moments of the day's running.
Rossi's team-mate Antonio Felix da Costa completed a good day for Arden Caterham in sixth. That meant the team, which took its first win last time out, had both cars in the top six in both sessions.
The championship's other contender, Ferrari junior Jules Bianchi, had a quiet day. After setting the 13th quickest time in the morning, he spent much of the afternoon session towards the bottom of the times. He got as high as 11th during his final run, but eventually ended up 15th.
Afternoon practice:Pos Driver Team Time Gap 1. Kevin Magnussen Carlin 1m47.416s 2. Alexander Rossi Arden Caterham 1m47.657s + 0.241s 3. Nick Yelloly Comtec 1m47.659s + 0.243s 4. Robin Frijns Fortec 1m48.017s + 0.601s 5. Sam Bird ISR 1m48.027s + 0.611s 6. Antonio Felix da Costa Arden Caterham 1m48.044s + 0.628s 7. Carlos Huertas Fortec 1m48.184s + 0.768s 8. Mikhail Aleshin RFR 1m48.211s + 0.795s 9. Andre Negrao Draco 1m48.309s + 0.893s 10. Nico Muller Draco 1m48.345s + 0.929s 11. Davide Rigon BVM Target 1m48.392s + 0.976s 12. Marco Sorensen Lotus 1m48.420s + 1.004s 13. Arthur Pic DAMS 1m48.438s + 1.022s 14. Daniil Move P1 1m48.464s + 1.048s 15. Jules Bianchi Tech 1 1m48.497s + 1.081s 16. Lucas Foresti DAMS 1m48.583s + 1.167s 17. Jake Rosenzweig ISR 1m48.698s + 1.282s 18. Daniel Abt Tech 1 1m48.783s + 1.367s 19. Vittorio Ghirelli Comtec 1m49.266s + 1.850s 20. Aaro Vainio RFR 1m49.390s + 1.974s 21. Kevin Korjus Lotus 1m49.562s + 2.146s 22. Nikolay Martsenko BVM Target 1m49.586s + 2.170s 23. Walter Grubmuller P1 1m49.772s + 2.356s 24. Yann Cunha Pons 1m49.829s + 2.413s 25. Zoel Amberg Pons 1m51.011s + 3.595s 26. Will Stevens Carlin Morning times:Pos Driver Team Time Gap 1. Nick Yelloly Comtec 1m48.964s 2. Arthur Pic DAMS 1m49.222s + 0.258s 3. Alexander Rossi Arden Caterham 1m49.418s + 0.454s 4. Kevin Magnussen Carlin 1m49.426s + 0.462s 5. Sam Bird ISR 1m49.493s + 0.529s 6. Antonio Felix da Costa Arden Caterham 1m49.628s + 0.664s 7. Kevin Korjus Lotus 1m49.661s + 0.697s 8. Nico Muller Draco 1m49.677s + 0.713s 9. Vittorio Ghirelli Comtec 1m49.750s + 0.786s 10. Carlos Huertas Fortec 1m49.920s + 0.956s 11. Aaro Vainio RFR 1m49.944s + 0.980s 12. Mikhail Aleshin RFR 1m50.015s + 1.051s 13. Jules Bianchi Tech 1 1m50.064s + 1.100s 14. Andre Negrao Draco 1m50.310s + 1.346s 15. Robin Frijns Fortec 1m50.374s + 1.410s 16. Marco Sorensen Lotus 1m50.383s + 1.419s 17. Daniil Move P1 1m50.451s + 1.487s 18. Daniel Abt Tech 1 1m50.559s + 1.595s 19. Davide Rigon BVM Target 1m50.577s + 1.613s 20. Walter Grubmuller P1 1m50.584s + 1.620s 21. Jake Rosenzweig ISR 1m50.752s + 1.788s 22. Lucas Foresti DAMS 1m51.261s + 2.297s 23. Nikolay Martsenko BVM Target 1m51.540s + 2.576s 24. Will Stevens Carlin 1m51.721s + 2.757s 25. Yann Cunha Pons 1m51.974s + 3.010s 26. Zoel Amberg Pons
The 2015 Formula Renault 3.5 season will be notable for being the last with the French company's backing but also produced a worthy champion in Oliver Rowland. PETER MILLS evaluates this year's crop of drivers
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