Ferrari's Kimi Raikkonen posted the fastest time on a track artificially soaked to test wet conditions as Lewis Hamilton's first week of testing fizzled to a premature end on Thursday.
Raikkonen's best time of 1min 20.872 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.
"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 tweeted.
New 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's time of 1min 19.705sec on Wednesday remained the fastest for the opening week of testing.
"Unfortunately the day was a little bit shorter than we were hoping for, but overall it has been a very good four days for us," said the Finn.
"As a team we really made the most out of this week. We've done a lot of mileage and I learned a lot."
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.
"I think Mercedes might still have an advantage on us in terms of power at the beginning of the season but we'll be catching up," warned Verstappen.
British driver Jolyon Palmer was third quickest for Renault.
The beleaguered McLaren 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.
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 on March 26 also takes place in Barcelona, from March 7-10.