Barcelona F1 test: Vettel fastest for Ferrari on opening day

The German clocked a 1m23.220s on the soft tyres and managed 103 laps to finish 0.117 seconds clear of Nico Rosberg, who had the highest lap tally with 119.

McLaren's Jenson Button, who led the way after the morning session, was third, half a second adrift.

Dry but chilly conditions greeted the teams on the first morning of the two-day test but temperatures gradually warmed up as the sun broke through.

Ferrari focused on one-lap pace in the morning, having struggled in Spanish Grand Prix qualifying, and Vettel completed a series of short runs on the soft and medium.

But it was Williams that caused a stir when it unveiled a radical new rear wing and modified front wing.

The team said the new parts, run by development driver Alex Lynn who finished ninth quickest, were focused on 2016 and '17, the latter of which will feature new bodywork rules kicking in.

Williams then reverted to its 2016-spec configuration for the afternoon, with Lynn completing 86 laps and ending the day 2.851s off the pace.

Romain Grosjean ran a new Haas chassis as he looks to get on top of his balance problems and ended up fourth, 0.662s adrift, after a late run on the ultra-soft tyres that will make their race debut next time out in Monaco.

Manor's Pascal Wehrlein used the super-softs to finish fifth quickest, one second off the pace, ahead of Red Bull's Daniel Ricciardo.

Toro Rosso's Pierre Gasly was seventh quickest, ahead of Force India development driver Alfonso Celis Jr.

Esteban Ocon, who gave Renault's new spec power unit its first outing, propped up the timesheets in 10th, 3.310s off the pace.

DAY ONE TEST TIMES