Lewis Hamilton's Mercedes emerged quickest in Thursday's morning session on the third day of pre-season testing at Bahrain's Sakhir circuit.
The British former world champion, who sat out Wednesday's testing, topped the timesheets with a lap of 1min 34.263 on soft tyres.
His fellow Briton, McLaren's Jenson Button, was next best on 1:34.976 with a gap then of over two seconds back to the rest of the pack headed by the Sauber of Mexican Esteban Gutierrez.
Hamilton's performance was further proof of Mercedes' bright showing in testing both here and at Jerez in Spain last month.
World champions Red Bull, who endured a torrid time at Jerez but have appeared in better shape at Sakhir, were placed seventh courtesy of Sebastian Vettel's new teammate Daniel Ricciardo.
Morning testing times
1. Lewis Hamilton (GBR/Mercedes) 1min 34.263sec, 2. Jenson Button (GBR/McLaren) 1:34.976, 3. Esteban Gutierrez (MEX/Sauber) 1:37.180, 4. Sergio Perez (MEX/Force India) 1:38.753, 5. Pastor Maldonado (VEN/Lotus) 1:39.642, 6. Daniel Ricciardo (AUS/Red Bull) 1:40.781, 7. Daniil Kvyat (RUS/Toro Rosso) 1:40.801, 8. Kimi R~CHECK~ikkonen (FIN/Ferrari) 1:41.336, 9. Marcus Ericsson (SWE/Caterham) 1:42.905, 10. Max Chilton (GBR/Marussia) 1:46.672