The Briton, driving for the iSport International squad this season, set his 1m46.678s best time two thirds of the way through the 30 minute session on the medium compound Pirelli tyres.
Palmer may have been bumped from the top spot not long after, but Valsecchi - on the hard tyre - locked up into the final hairpin on his best lap. The DAMS driver was thus forced to accept second fastest, just 0.164 seconds slower than Palmer.
Carlin's Tom Chilton was 0.638s away from the pace in third ahead of one of the championship favourites Giedo van der Garde (Caterham), Fabio Onidi (Coloni) and early pacesetter Felipe Nasr in the second DAMS car.
Another to top the times early in the session, Luiz Razia, was seventh for Arden ahead of ART Lotus's James Calado, Coloni's Stefano Coletti and Josef Kral, driving for Addax.
Kral's team-mate Johnny Cecotto Jr caught the attention of the stewards when he and Esteban Gutierrez (ART Lotus) made contact at Turn 12 as the Venezualen tried to pass the Mexican around the outside.
Cecotto was travelling at a much faster pace, but appeared to go down a gap that was not wide enough for a Dallara, the impact damaging Gutierrez's car and forcing him to pull off the track with only a third of the session complete. The incident was under investigation.
Also being investigated by the stewards was Trident's Stephane Richelmi for a separate issue.
1. Jolyon Palmer iSport 1m46.514s
2. Davide Valsecchi DAMS 1m46.678s + 0.164s
3. Max Chilton Carlin 1m47.152s + 0.638s
4. Giedo van der Garde Caterham 1m47.229s + 0.715s
5. Fabio Onidi Coloni 1m47.318s + 0.804s
6. Felipe Nasr DAMS 1m47.360s + 0.846s
7. Luiz Razia Arden 1m47.418s + 0.904s
8. James Calado Lotus 1m47.532s + 1.018s
9. Stefano Coletti Coloni 1m47.533s + 1.019s
10. Josef Kral Addax 1m47.580s + 1.066s
11. Fabio Leimer Racing Engineering 1m47.616s + 1.102s
12. Johnny Cecotto Jr Addax 1m47.637s + 1.123s
13. Esteban Gutierrez Lotus 1m47.639s + 1.125s
14. Nathanael Berthon Racing Engineering 1m47.644s + 1.130s
15. Jon Lancaster Ocean 1m47.681s + 1.167s
16. Fabrizio Crestani Lazarus 1m47.699s + 1.185s
17. Stephane Richelmi Trident 1m47.862s + 1.348s
18. Simon Trummer Arden 1m48.246s + 1.732s
19. Rio Haryanto Carlin 1m48.259s + 1.745s
20. Marcus Ericsson iSport 1m48.326s + 1.812s
21. Nigel Melker Ocean 1m48.437s + 1.923s
22. Tom Dillmann Rapax 1m48.447s + 1.933s
23. Julian Leal Trident 1m48.746s + 2.232s
24. Rodolfo Gonzalez Caterham 1m48.764s + 2.250s
25. Ricardo Teixeira Rapax 1m50.549s + 4.035s
26. Giancarlo Serenelli Lazarus 1m52.306s + 5.792s