Kimi Raikkonen finished top of the timesheets in FP3 as both Mercedes cars struggled to make an impression, while Sebastian Vettel suffered a disrupted session.
The Finn was P1 with a 1:29.868, five tenths quicker than the two Red Bulls of Max Verstappen and Daniel Ricciardo. Lewis Hamilton was a distant P4 after struggling to get to grips with the circuit.
A broken bargeboard and then "something quite bad" happened to Vettel's car to leave him unable to complete a full qualifying simulation run in P5.
Valtteri Bottas was also unable to threaten Raikkonen's best, finishing nine tenths off the pace.
Nico Hulkenberg and Carlos Sainz finished in the top 10 for Renault, as did Pierre Gasly who continues to showcase Honda's surprising pace in the desert so far.
Fernando Alonso finished in close quarters, though, in P10.
There was some minor drama for Vettel in the opening stages of FP3 as the turning vanes on his right sidepod came loose and started to flap around in the Bahrain sun.
As the Ferrari mechanics got to work on the repair, it was Mercedes setting the early pace out on track with Bottas and Hamilton immediately lapping in the 1:30 region.
Verstappen then split the Mercedes pair in P2 with 25 minutes left on the clock, around the same time that Vettel was able to head back out on track.
He soon went quickest of everyone in the first and final sectors, shaving 0.062s off Bottas' best and lowering the benchmark a little more on an old set of supersofts.
The pace then began to heat up as teams turned their attention to their final qualifying simulation programmes. With a new set of supersofts strapped on, Raikkonen posted a 1:29.868 to give the other leading contenders something to aim at.
Hamilton and Bottas struggled on their first attempt to topple Raikkonen, the former running wide at the final corner which was a pretty common scene across the field.
It was a similar outcome on Hamilton's second hot lap but, a few seconds later, Vettel reported that something "quite bad" happened to his car at Turn 11 and 12.
He was told to box immediately and was unable to complete a proper qualifying sim run.
Red Bull's late attack saw both Max Verstappen and Daniel Ricciardo narrow the gap to Raikkonen to half a second, the Dutchman then had a close call with Raikkonen as the Finn came out of the pit lane.
Mercedes continued to make no real impression as the checkered flag waved.
Qualifying under the night sky will begin at 1800 local time.
1 Kimi Raikkonen Ferrari 1'29.868
2 Max Verstappen Red Bull 1'30.393 0.525
3 Daniel Ricciardo Red Bull 1'30.452 0.584
4 Lewis Hamilton Mercedes 1'30.691 0.823
5 Sebastian Vettel Ferrari 1'30.719 0.851
6 Valtteri Bottas Mercedes 1'30.781 0.913
7 Nico Hulkenberg Renault 1'31.144 1.276
8 Carlos Sainz Renault 1'31.200 1.332
9 Pierre Gasly Toro Rosso 1'31.438 1.570
10 Fernando Alonso McLaren 1'31.445 1.577
11 Brendon Hartley Toro Rosso 1'31.460 1.592
12 Romain Grosjean Haas 1'31.513 1.645
13 Esteban Ocon Force India 1'31.554 1.686
14 Sergio Perez Force India 1'31.564 1.696
15 Kevin Magnussen Haas 1'31.737 1.869
16 Marcus Ericsson Sauber 1'31.859 1.991
17 Stoffel Vandoorne McLaren 1'31.860 1.992
18 Charles Leclerc Sauber 1'32.047 2.179
19 Sergey Sirotkin Williams 1'32.463 2.595
20 Lance Stroll Williams 1'32.865 2.997