The Malaysian driver led the way in the morning running, and his benchmark was not bettered in the afternoon session as series rookie Oliver Rowland fell just one tenth of a second short of going quickest overall.
Jaafar was not as much of a factor in the afternoon, which he put down to trying "something different" with the car set-up that did not work out.
Rowland, who has been a regular frontrunner in testing this winter with Fortec, set his best lap with just half an hour remaining in the day. He revealed that he went off the track on his final lap.
Fellow Formula Renault 2.0 graduate Pierre Gasly - last year's FR Eurocup champion - was another to miss out on a late improvement as a red flag in the closing minutes halted the Red Bull junior on a lap which he felt would have put him in the top five overall.
Will Stevens ended the day third-fastest with his best lap from the morning, while Rowland's closest challengers in the afternoon - Marlon Stockinger, Carlos Sainz Jr and Sergey Sirotkin - completed the top six for the day.
Only 23 of this season's 26 cars were in action at Jerez. Championship-winning team Carlin has sat out all of pre-season so far, while Comtec Racing only ran one car with Nikolay Martsenko.
COMBINED DAY ONE TIMES:
Pos Driver Team Time Gap 1. Jazeman Jaafar ISR 1m26.840s 2. Oliver Rowland Fortec 1m26.986s +0.146s 3. Will Stevens Strakka 1m26.998s +0.158s 4. Marlon Stockinger Lotus 1m27.002s +0.162s 5. Carlos Sainz DAMS 1m27.003s +0.163s 6. Sergey Sirotkin Fortec 1m27.025s +0.185s 7. Matias Laine Strakka 1m27.027s +0.187s 8. Matthieu Vaxiviere Lotus 1m27.051s +0.211s 9. Norman Nato DAMS 1m27.079s +0.239s 10. Nigel Melker ISR 1m27.186s +0.346s 11. Nikolay Martsenko Comtec 1m27.281s +0.441s 12. Pierre Gasly Arden 1m27.313s +0.473s 13. Luca Ghiotto Draco 1m27.340s +0.500s 14. Pietro Fantin Draco 1m27.391s +0.551s 15. Roberto Merhi Zeta 1m27.655s +0.815s 16. Marco Sorensen Tech 1 1m27.656s +0.816s 17. Tio Ellinas Tech 1 1m27.670s +0.830s 18. Will Buller Arden 1m27.729s +0.889s 19. Meindert van Buuren Pons 1m27.881s +1.041s 20. Zoel Amberg AVF 1m27.918s +1.078s 21. Beitske Visser AVF 1m28.605s +1.765s 22. Roman Mavlanov Zeta 1m28.873s +2.033s 23. Robert Visoiu Pons 1m29.115s +2.275s
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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