The two Danes were locked in combat for the top spot from the moment they took to the track for their second runs.
Both had several turns at the top as they improved on almost every lap they completed, which edged them away from the threat of those behind.
The session appeared to be building to a fantastic finish, with Magnussen (second at the time) just getting across the line before the chequered flag, and Sorensen looking set to improve his benchmark on his final lap.
Sorensen missed out on bettering his pole time by less than a tenth of a second, and his Lotus team then had to watch on as Magnussen set a personal best first sector.
But the McLaren junior's lap fell away in the middle sector, and he aborted the run to return to the pits.
Behind the Danish front row, Nigel Melker was best of the rest, while title outsider Will Stevens boosted his chances of making up ground by slotting onto the second row in the closing moments.
Early pacesetter Arthur Pic eventually took fifth place, just ahead of championship leader Stoffel Vandoorne and Red Bull junior Antonio Felix da Costa.
Da Costa appeared to have a frustrating session, only briefly getting as high as third in the order before he was quickly shuffled back.
Pos Driver Team Time Gap Laps 1. Marco Sorensen Lotus 1m15.976s 16 2. Kevin Magnussen DAMS 1m16.048s +0.072s 18 3. Nigel Melker Tech 1 1m16.294s +0.318s 17 4. Will Stevens P1/Strakka 1m16.363s +0.387s 17 5. Arthur Pic AV 1m16.377s +0.401s 16 6. Stoffel Vandoorne Fortec 1m16.527s +0.551s 18 7. Antonio Felix da Costa Arden Caterham 1m16.616s +0.640s 18 8. Nikolay Martsenko Pons 1m16.759s +0.783s 17 9. Norman Nato DAMS 1m16.764s +0.788s 17 10. Marlon Stockinger Lotus 1m16.777s +0.801s 16 11. Sergey Sirotkin ISR 1m16.782s +0.806s 15 12. Will Buller Zeta Corse 1m16.854s +0.878s 15 13. Carlos Huertas Carlin 1m16.903s +0.927s 17 14. Nico Muller Draco 1m16.904s +0.928s 16 15. Yann Cunha AV 1m16.919s +0.943s 16 16. Christopher Zanella ISR 1m17.069s +1.093s 16 17. Oliver Webb Fortec 1m17.080s +1.104s 18 18. Pietro Fantin Arden Caterham 1m17.093s +1.117s 17 19. Andre Negrao Draco 1m17.160s +1.184s 17 20. Zoel Amberg Pons 1m17.339s +1.363s 17 21. Mikhail Aleshin Tech 1 1m17.458s +1.482s 17 22. Daniil Move Comtec 1m17.769s +1.793s 18 23. Riccardo Agostini Zeta Corse 1m17.886s +1.910s 16 24. Lucas Foresti Comtec 1m17.891s +1.915s 17 25. Matias Laine P1/Strakka 1m18.262s +2.286s 17 26. Jazeman Jaafar Carlin 1m19.162s +3.186s 6
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