Barcelona - Kimi Raikkonen posted the fastest time on a track artificially soaked to test wet conditions as an electrical fault brought Lewis Hamilton's first week of testing to a premature end on Thursday.
Raikkonen's best time of 1min 20.872 in his Ferrari came late in the day in Barcelona as the track dried out after trucks dumped water on the surface overnight and again during the lunch break.
Three-time world champion Hamilton didn't even get out of the Mercedes garage as an electrical fault prevented him from running as scheduled during the morning session.
"Electrical fault kept us in the garage this morning, so I've decided with the team not to drive today as I wouldn't have learned much," Hamilton posted on his Twitter account.
"Shame not to drive but it's been a great few days. The guys have done an awesome job. Can't wait to be back in the car next week!"
Hamilton's Mercedes teammate Valtteri Bottas did manage to run in the afternoon, but was way down the timesheets in eighth fastest for his 68 laps.
However, Bottas' time of 1min 19.705sec on Wednesday remained the fastest of the week.
In a recurring theme over the first few days of pre-season testing, Red Bull were the best of the rest behind Ferrari and Mercedes as Dutch wonder kid Max Verstappen was second fastest.
British driver Jolyon Palmer was third quickest for Renault.
The beleaguered McLaren-Honda team had a more positive day in terms of mileage as Belgian rookie Stoffel Vandoorne completed 67 laps, but F1's fallen giants remain well off the pace of those at the front of the grid.
Williams also called an early end to their first test after damage suffered to the FW40 in rookie Lance Stroll's crash on Wednesday.
"A second chassis will be prepared at track this afternoon, as originally planned, with the team aiming to be back on track for the second test next week," Williams said in a statement.
The second and final four-day test before the season opening Grand Prix in Australia also takes place in Barcelona from March 7-10.