Sebastian Vettel and Kimi Raikkonen laid down a marker for Ferrari at the Spanish Grand Prix by completing a one-two in first free practice, while Max Verstappen placed sixth in a solid first outing for Red Bull.
Four-time world champion Vettel and Raikkonen were the only duo to run the soft tyres at the Circuit de Barcelona-Catalunya, a tactic that saw them place ahead of championship leader Nico Rosberg and defending champion Lewis Hamilton for Mercedes.
Vettel, who earlier this week said it is too soon to say the Formula One title race is a one-horse race despite Rosberg winning all four meets in 2016, clocked a fastest time of one minute and 23.951 seconds.
The German tried to sneak one final lap and beat the red light, only to be quickly wheeled back in by the mechanics with Vettel fuming "This is a joke".
Raikkonen was just 0.138secs adrift of his team-mate, while Rosberg was marginally quicker than Lewis Hamilton, who was keen to test the limits of the track and went slightly off at Turn One early in the session.
It was a fine start for Verstappen, who was promoted from Red Bull's sister team Toro Rosso with Daniil Kvyat demoted after an error strewn start to the season, including shunting Vettel at Kvyat's home grand prix in Russia last time out.
The Belgian complained of acceleration issues early on, but they seemingly eased as he placed sixth, just 0.169secs slower than team-mate Daniel Ricciardo.
Fernando Alonso was backed heavily by the Spanish crowd, and the McLaren man was 10th fastest in FP1.
1 Sebastian Vettel (Ferrari) 1:23.951
2 Kimi Raikkonen (Ferrari) 1:24.089
3 Nico Rosberg (Mercedes) 1:24.454
4 Lewis Hamilton (Mercedes) 1:34.611
5 Daniel Ricciardo (Red Bull) 1:25.416
6 Max Verstappen (Red Bull) 1:25.585
7 Valtteri Bottas (Williams) 1:25.672
8 Carlos Sainz Jr (Toro Rosso) 1:26.078
9 Felipe Massa (Williams) 1:26.186
10 Fernando Alonso (McLaren) 1:26.243