Click here for full results from the opening day of F1 pre-season testing
Sebastian Vettel has ended the opening day of F1 pre-season testing quickest while Ferrari reignited its battle for top spot with Mercedes' Lewis Hamilton close behind having notched up a marathon total of laps.
After Vettel and Hamilton had traded fastest lap times during the opening phases of the first day of 2016 testing, the German set a benchmark of 1m 24.939s which remained unbeaten for the rest of the day while the Mercedes driver opted to concentrate on longer stints.
A brief red flag halted proceedings towards the end of the morning session after Romain Grosjean and new team Haas suffered a dramatic front wing failure along the main straight. The French driver was able to steer the VF-16 back to the garage to allow the US team to undertake a thorough investigation into the accident and was able to finish the day with some extra laps in the final two hours.
With the personal best lap times remaining largely unchanged during the middle period of the day, Hamilton banked an impressive amount of laps in the 1m 26s bracket to demonstrate the new Mercedes W07 had lost none of its predecessor's reliability and consistency.
However, it is Ferrari and Vettel who walk away from the opening day with the headlines having also completed 69 laps in total and looks set to take the fight to Mercedes in 2016.
Further back, Red Bull's new TAG-Heuer branded engine impressed after Daniel Ricciardo claimed third on the timesheet while completing 86 laps after edging Williams' Valtteri Bottas into fourth during the afternoon session.
After a frantic start to the opening F1 test with a number of team presentations and car launches, the action got off to a tepid start due to the damp circuit forcing gentle installation laps. The sunshine quickly broke through at the Circuit de Catalunya allowing teams to get to grips with the 2016 challengers on a dry track.
Force India's new development driver Alfonso Celis was handed the honour of turning the first laps in the new VJM09 and after an unspectacular start he crept up the timesheet to end the day fifth quickest.
Despite being shuffled down to sixth late on, McLaren-Honda's Jenson Button might be happier with his day's work than at any point during last season having completed 84 laps with the quickest time of 1m 26.735s.
Carlos Sainz ran a relatively quiet day in the all-blue Toro Rosso ending the day seventh ahead of Marcus Ericsson in the 2015 Sauber, with the team's new car expected to arrive in time for the second Barcelona test.
The new-look MRT and its combination of Mercedes power, Williams transmission and DTM champion Pascal Wehrlein got off to a tentative start but made solid progress at its lap times to sneak in front of Grosjean late on, while the Renault of Jolyon Palmer was left lagging at the back and a second off of new boys Haas.