Kimi Raikkonen topped the leaderboard ahead of Ferrari teammate Sebastian Vettel in the second practice session for the Bahrain Grand Prix after Australia's Daniel Ricciardo had given Red Bull an early boost by clocking the fastest time in the opening session.
But Lewis Hamilton's hopes of victory on Sunday have taken a major dent after he was hit with a five-place grid penalty.
Defending champion Hamilton was bidding to get his title charge back on track this weekend after losing out to Vettel at the season opener in Australia a fortnight ago.
But he will now be bumped down the order following an unscheduled gearbox change on his Mercedes.
It means the Briton will start only sixth even if he manages to post the quickest time in Saturday's qualifying.
Raikkonen and Vettel were up front in Friday's second practice as cooler temperatures and nightfall matched the conditions for Sunday evening's race.
Raikkonen's time of one minute, 29.8 seconds on the 5.4km desert circuit was a fraction quicker than Vettel's.
Hamilton, who had a patchy fifth-placed first practice session, again looked short of speed as he finished fourth in the second outing, just behind Mercedes teammate Valtteri Bottas.
In a boost for Ferrari, both Mercedes cars were more than half a second slower than the best lap set by Raikkonen, who would be investigated by race stewards for an unsafe car release following a pitstop.
Max Verstappen, who failed to register a time in the first session, was fifth, ahead of Ricciardo.
Earlier in the day, Ricciardo was 0.3 seconds quicker than Bottas and 0.4 seconds faster than Raikkonen.
Verstappen's car lost power and stopped on the track in the first session. He got out and helped stewards wheel it back to the team garage. The Dutch driver spun early into the season-opening Australian GP two weeks ago, finishing in sixth place.
Verstappen complained about a lack of speed in his Red Bull on Friday.
"Why am I so slow on the straights? It's unbelievable," he said on his team radio.
There will be a third and final practice session on Saturday before qualifying.
Vettel won in Melbourne, profiting from an error by Mercedes to finish ahead of Hamilton, who was leading from pole.
