KimiRaikkonen led his championship-leading team mate Sebastian Vettel in a Ferrari one-two at the top of the timesheets in floodlit free practice for the Bahrain Grand Prix on Friday.
The Finn was summoned to the stewards afterwards for an unsafe release from the pits but escaped a grid penalty with Ferrari picking up a 5,000 euro ($6,136.50) fine instead for the misdemeanour.
The team had told Raikkonen immediately after the practice stop that there was a loose wheel on the car and he stopped as soon as it was safe to do so.
Raikkonen, who was third in the opening afternoon session led by Red Bull's Daniel Ricciardo, lapped the 5.4km Sakhir circuit in one minute 29.817 seconds.
Vettel, winner last year in Bahrain, was a mere 0.011 seconds slower.
The two Ferraris were the only ones to dip into the one minute 29 second bracket, with Valtteri Bottas half a second off Raikkonen's benchmark with what was reigning champions Mercedes’ best effort.
The Finn, who had been second on the timesheets in the opening practice, ended the day third quickest with Lewis Hamilton fifth and fourth in the respective sessions.
"Although we were untroubled by any reliability issues, and we ran through our programme as expected, it wasn't our best day from a performance point of view," said Mercedes technical head James Allison.
"We've got more to do overnight and in the session tomorrow to give us a car that will allow us to have a good fight in qualifying and on Sunday.
"The base is okay but we have not yet found the sort of edge that we had in Melbourne."
Vettel snatched an opportunistic win from Hamilton in Formula One’s season opener in Australia two weeks ago, taking advantage of a timely virtual safety car to pit and stay ahead of the Briton who had led from pole.
Hamilton's Mercedes was clearly fastest in Melbourne and the four-times champion arrived in Bahrain as favourite to make up the lost ground.
His best effort on Friday was 0.655 seconds slower than Raikkonen, however, with at least some of that down to the 33-year-old running into traffic on his flying lap.
Hamilton remains on course, though, to equal Raikkonen’s record of 27 consecutive finishes in the points.
"It's been a normal Friday, we've got through all our programme. It looks very close between all the teams and we definitely have got some work to do to try and see if we can eke out to be ahead of the others," said Hamilton.
Max Verstappen ended the day fifth fastest ahead of Red Bull team mate Daniel Ricciardo.
The former champions had book-ended the timesheets in the afternoon, with Ricciardo fastest and Verstappen at the bottom having failed to set a time after being sidelined by an electrical issue.
The Dutchman got out and helped marshals push the car back to the pitlane.
Nico Hulkenberg was seventh fastest in the Renault ahead of Toro Rosso’s Pierre Gasly while McLaren pair Fernando Alonso and Stoffel Vandoorne rounded out the top 10.
Friday’s two 90-minute sessions were relatively uneventful although Bottas, on a slow lap, almost collided with Ricciardo who was going quickly.