Nico Rosberg set the pace as Mercedes used soft tyres for the first time in 2016 pre-season Formula 1 testing at Barcelona on Tuesday morning.
The world champion team chose not to run any soft tyres last week as it focused on logging mileage in search of reliability, with Lewis Hamilton and Rosberg managing 675 laps between them.
But on day one of the final four-day pre-season test, Rosberg bolted on a set of softs with 45 minutes to go until lunch and pumped in a 1m23.022s.
That time is around two tenths of a second slower than the best time from last week, set by Ferrari's Sebastian Vettel on the ultra-soft tyres.
Kimi Raikkonen was Rosberg's closest challenger, but his best set on the medium tyres left him 1.814s off the pace.
Rosberg, who will hand the car over to Hamilton for the afternoon, once again led the way in terms of mileage covered with 82 laps.
That tally was nearly double the amount of laps Raikkonen managed to log in the Ferrari.
Fernando Alonso was the only driver other than Rosberg to run the softs, with the Spaniard going third quickest, 2.230s off the pace.
McLaren-Honda focused on drivability and mapping of the Honda power unit in balance to the car and clocked up 50 laps.
Alonso was then responsible for the first and only red flag of the day when he stopped at the pit exit with less than a minute to go.
Valtteri Bottas was fourth quickest for Williams, ahead of Max Verstappen in the now 2016-liveried Toro Rosso and the Force India of Nico Hulkenberg.
Red Bull's Daniil Kvyat was seventh with just 22 laps while eighth-placed Esteban Gutierrez only managed one more than that.
Felipe Nasr put the 2016-spec Sauber through its paces for the first time, with the Swiss team focusing on aero runs and system checks.
Kevin Magnussen was 10th quickest ahead of Rio Haryanto, whose Manor suffered an oil leak that confined him to the garage for most of the morning.
TUESDAY MORNING TIMES:
|5||Max Verstappen||Toro Rosso/Ferrari||1m25.356ss||2.334s||59|
|6||Nico Hulkenberg||Force India/Mercedes||1m25.954ss||2.932s||50|
|7||Daniil Kvyat||Red Bull/TAG Heuer||1m26.227ss||3.205s||22|