Ending the day at the top of the charts didn't seem to matter to Sebastian Vettel, but the new addition to the Ferrari ranks is happy with the car.
McLaren programme ended early after the engineers and mechanics were unable to resolve a technical issue.
Marcus Ericsson was able to complete 73 mainly trouble-free laps.
Carlos Sainz: "I felt good in the car today, I was constantly improving, lap after lap."
Kate Walker is your guide to a team-by-team run-down of what happened on the opening day of official Formula One testing at Jerez in Spain.
There was a sense of achievement felt among the team at the end of the day.
Eric Boullier is confident that the gremlins are fixable, possibly even by tomorrow.
Valtteri Bottas: "There are a lot of strengths in this car and we’ve made good progress in just one day, so I am very pleased."
McLaren and Honda know that their road to glory may be a tough one.
The F1 W06 Hybrid ran trouble-free throughout the day
Ferrari leads the way after the opening day of action at Jerez.
The team showed strong development throughout last season and aim to continue this as the regulations show minimal changes for the new season ahead.
Drivers Lewis Hamilton and Nico Rosberg revealed the seventh Silver Arrow...
No fireworks from new engine so far, as team logs laps with brand new MP4-30 contender.
Formula One superstars kick-off 2015 season at Jerez for pre-season testing.
Toto Wolff discusses the development of the W06.
Team boss sets high target for its new pair of rookie drivers.
Seventeen-year-old Formula One rookie sets himself a huge target for opening Grand Prix.
Wraps come off STR10 as Sainz and Verstappen gear up for their Formula One debuts.