The Finn leapfrogged Lewis Hamilton's Mercedes one hour from the day's end, with the Briton's session ending prematurely after a front wing failure sent him crashing into the Turn 1 barriers.
Hamilton had previously been the first man to venture out on track and the first man to set a competitive time, and was more than five seconds clear at the head of the timesheets when he suffered the accident.
He was unable to return, but remained upbeat about the team's day one showing.
At the time of Hamilton's crash, which came at midday, Jean-Eric Vergne had been Hamilton's closest challenger in terms of both lap count and time, even if his deficit was sizeable.
His day was also curtailed early however when the Toro Rosso developed problems heading into the final two hours.
In their absence, Raikkonen rose to the fore, clocking 31 laps and setting the fastest time, a 1m27.104s.
The Finn's day had started auspiciously when his F14 T stopped just five corners into its maiden installation lap at Jerez, a halt the team described as precautionary.
He was not alone in hitting trouble: as well as Hamilton and Vergne's issues, Sergio Perez brought about a fourth red flag when he too stopped on the first lap with new team Force India.
The Mexican eventually clocked 10 timed laps, setting his best - a 1m33.161s - as the chequered flag fell.
That put him fourth overall, six seconds off Raikkonen's benchmark and four off Valtteri Bottas, who ended the day third for Williams.
The team was only able to get its car out in the final part of the day, but managed seven timed laps.
That left Vergne down in fifth, but still comfortably ahead of the Sauber's Esteban Gutierrez, the day's final classified runner.
As well as Vettel, Caterham's Marcus Ericsson also got out but failed to set a time.
The Swede managed just one exploratory lap in the CT05, which was unveiled late in the afternoon.
McLaren was not able to join the fray, suffering with electronic/hydraulic issues, while Marussia is not expected to run until Thursday at the earliest, having elected to keep its car in the UK to deal with a late technical glitch.