Ferrari's Kimi Raikkonen left struggling Mercedes trailing in final practice at the Bahrain Grand Prix.
The Finn was 0.5 seconds ahead of the Red Bulls of Max Verstappen and Daniel Ricciardo, while Lewis Hamilton was only fourth in his difficult Mercedes.
Hamilton headed Ferrari's Sebastian Vettel by 0.028secs but the German had difficulties with loose bodywork early on and engine problems later.
Hamilton has a difficult race with a five-place grid penalty confirmed.
If he qualifies fastest later on Saturday, Hamilton will start sixth at best but in final practice the Mercedes looks to be the third fastest car around the Sakhir track.
Hamilton was clearly struggling with balance, locking wheels, suffering from under-steer in some corners and from oversteer in others.
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His team-mate Valtteri Bottas was in similar trouble and ended up sixth quickest, 0.09secs slower than Hamilton.
Raikkonen has appeared so far this weekend to have an edge on Vettel would likely have joined Raikkonen at the top of the timings had his session not been hit by a series of problems.
A piece of bodywork beside the cockpit became loose as Vettel started his first run, he went quickest after it was repaired but then aborted his final run complaining of engine drivability issues.
Vettel's problems allowed the Red Bulls to leap into second and third places, Verstappen 0.525secs behind Raikkonen and just 0.059secs quicker than Ricciardo.
Behind the big three, Renault's Nico Hulkenberg and Carlos Sainz were next, the German 0.751secs off the pace and 0.056secs ahead of the Spaniard.
And Toro Rosso continued to impress, Pierre Gasly ninth fastest and 0.007secs ahead of McLaren's Fernando Alonso, whose team dropped the Honda engine now used by Toro Rosso last year claiming that it was holding them back.
Gasly's team-mate Brendon Hartley was 11th ahead of the Haas of Romain Grosjean.
Williams are having a torrid weekend, Sergey Sirotkin and Lance Stroll at the back, the Russian nearly half a second off the next slowest car but 0.4secs up on his team-mate.