Nico Rosberg set the pace in opening practice for the Bahrain Grand Prix on Friday, with Mercedes in a league of its own.
The Australian Grand Prix winner posted a best lap of 1:32.294 using soft tyres to finish over half a second clear of teammate Lewis Hamilton, second quickest.
Rosberg's time was over five seconds faster than the benchmark set during FP1 in last year's event.
Kimi Raikkonen was the fastest of the non-Mercedes drivers in third, but the Ferrari man finished over 1.8 seconds behind Rosberg.
Red Bull's Daniel Ricciardo was over two seconds off the pace in fourth, ahead of teammate Daniil Kvyat.
Force India's Nico Hulkenberg finished in sixth, the German followed by Toro Rosso drivers Carlos Sainz and Max Verstappen.
Romain Grosjean continued to show promise in the Haas, posting the ninth fastest time ahead of Williams' Felipe Massa.
Sebastian Vettel finished 11th in the second Ferrari, nearly three seconds off Rosberg's pace.
Stoffel Vandoorne made his debut in a grand prix weekend after being drafted in to replace Fernando Alonso at McLaren.
The Belgian wound up 18th, nearly a second behind teammate Jenson Button.
Alfonso Celis was back in action in the Force India, replacing Sergio Perez for the first session. The Mexican took 21st.
It took nearly 15 minutes for the first driver to appear on the timesheets, when Pascal Wehrlein completed the first timed lap in the Manor.
Hamilton and Rosberg were the last men to take to the track - after the 15-minute mark - but the German was quick to move to the top of the times with a 1:33.592 on soft Pirelli tyres.
His teammate moved to second moments later, the Mercedes duo nearly two seconds clear of Button, their closest rival at that point.
It took until the final quarter of the session for a driver to get closer to the Mercedes pair, with Ricciardo jumping up to third position, 0.869s seconds off Rosberg's pace with a run on softs.
Ricciardo's teammate Kvyat also improved to move to fourth as the session entered the final 30 minutes.
With 20 minutes left, both Hamilton and Rosberg left the pits for another run of softs, and immediately went quicker, with the German lapping in 1:32.294, over half a second faster than his teammate, the only other driver in the 1:32s.