Lewis Hamilton finished outside the top three in both of Friday's practice sessions for the Bahrain Grand Prix as rivals Ferrari set the pace.
Defending champion Hamilton, who missed out on victory at the curtain raiser in Australia a fortnight ago, finished only fifth and then fourth in his Mercedes as Ferrari laid down the gauntlet.
Kimi Raikkonen set a quickest lap of one minute and 29.817 seconds at the Bahrain International Circuit to finish marginally faster that team-mate and championship leader Sebastian Vettel.
Hamilton had to settle for fourth - more than half-a-second adrift of Raikkonen - with his Mercedes team-mate Valtteri Bottas in third.
Red Bull's Daniel Ricciardo was fastest in the opening running here in the desert, but the Australian had to make do with sixth under the lights of the Sakhir circuit in the second session.
Max Verstappen, who missed the entirety of the first 90-minute session with a power problem, returned to set the fifth-best time, albeit nearly one second slower than Raikkonen.
Defending champion Hamilton was in control of the opening race in Melbourne a fortnight ago before a timing error by his Mercedes team gift-wrapped victory to Vettel during a safety car period.
Vettel won here last year, with Ferrari boasting the more complete package in the warm temperatures, and - on the evidence of practice at least - Hamilton and his Mercedes team may have their work cut out to prevent Ferrari from taking pole position on Saturday.
Hamilton remains upbeat however, that he is in the title fight as he pursues a fifth world championship crown.
Reflecting on the pain of Melbourne, the 33-year-old Englishman said: "I guess if we had started third and finished second in Australia it would have been a different feeling. You never want to move backwards so it was difficult for us all.
"Everyone in the team felt the same pain and we all sat together at the airport lounge after the race and had a drink, but we were incredibly unified.
"Some individuals would have had more sleepless nights than others maybe, but we come here strong and positive and with the right direction as how to move forward. We are still there in the fight."
Outside of the sport's top-three teams, Nico Hulkenberg was seventh in second practice for Renault ahead of Toro Rosso's Pierre Gasly.
Despite their move to Renault engines, McLaren remain off the pace of the front-runners with Fernando Alonso ninth, some 1.4 seconds off Raikkonen's lap.
- Daniel Ricciardo (Aus) Red Bull 1min 31.060secs
- Valtteri Bottas (Fin) Mercedes GP 1:31.364
- Kimi Raikkonen (Fin) Ferrari 1:31.458
4 Sebastian Vettel (Ger) Ferrari 1:31.470, 5 Lewis Hamilton (Gbr) Mercedes GP 1:32.272, 6 Romain Grosjean (Fra) Haas F1 1:32.516, 7 Pierre Gasly (Fra) Scuderia Toro Rosso 1:32.779, 8 Carlos Sainz (Spa) Renault 1:32.885, 9 Kevin Magnussen (Den) Haas F1 1:32.971, 10 Nico Hulkenberg (Ger) Renault 1:33.104, 11 Fernando Alonso (Spa) McLaren 1:33.223, 12 Charles Leclerc (Mon) Sauber-Ferrari 1:33.278, 13 Stoffel Vandoorne (Bel) McLaren 1:33.364, 14 Lance Stroll (Can) Williams 1:33.379, 15 Sergey Sirotkin (Rus) Williams 1:33.467, 16 Brendon Hartley (Nzl) Scuderia Toro Rosso 1:33.497, 17 Marcus Ericsson (Swe) Sauber-Ferrari 1:33.508, 18 Sergio Perez (Mex) Force India 1:33.662, 19 Esteban Ocon (Fra) Force India 1:33.794, 20 Max Verstappen (Ned) Red Bull No Time
- Kimi Raikkonen (Fin) Ferrari 1min 29.817secs
- Sebastian Vettel (Ger) Ferrari 1:29.828
- Valtteri Bottas (Fin) Mercedes GP 1:30.380
4 Lewis Hamilton (Gbr) Mercedes GP 1:30.472, 5 Max Verstappen (Ned) Red Bull 1:30.745, 6 Daniel Ricciardo (Aus) Red Bull 1:30.751, 7 Nico Hulkenberg (Ger) Renault 1:31.220, 8 Pierre Gasly (Fra) Scuderia Toro Rosso 1:31.232, 9 Fernando Alonso (Spa) McLaren 1:31.282, 10 Stoffel Vandoorne (Bel) McLaren 1:31.422, 11 Romain Grosjean (Fra) Haas F1 1:31.591, 12 Carlos Sainz (Spa) Renault 1:31.601, 13 Esteban Ocon (Fra) Force India 1:31.809, 14 Sergio Perez (Mex) Force India 1:31.868, 15 Kevin Magnussen (Den) Haas F1 1:31.969, 16 Charles Leclerc (Fra) Sauber-Ferrari 1:32.372, 17 Lance Stroll (Can) Williams 1:32.382, 18 Sergey Sirotkin (Rus) Williams 1:32.474, 19 Marcus Ericsson (Swe) Sauber-Ferrari 1:32.733, 20 Brendon Hartley (Nzl) Scuderia Toro Rosso