London: Four-time world champions Sebastian Vettel sent an early season warning to double world champions Mercedes by clocking the fastest time on his first day of testing with Ferrari in Jerez on Sunday.
The German was the first man out on the track, even sending a message by overtaking Nico Rosberg in the pit lane on the way out for his first lap in the SF15-T Ferrari.
It wasn`t until well into the afternoon that he surpassed Rosberg on the track, though, as he posted a best time of 1min 22.690secs during his 60 laps.
Vettel`s positive opening day was in stark contrast to his disastrous test in Jerez during a troubled final season with Red Bull last year when he lodged just 11 laps over two days.
It was also a good day for Sauber as Markus Ericsson was surprisingly also faster than Rosberg.
However, the Mercedes engines were still dominant when it came to time out on the track as Rosberg racked up 157 laps and last season`s surprise package Valteri Bottas completed 73.
The biggest strugglers on the opening day of the four-day session in southern Spain were McLaren as their new Honda-powered MP4-30 could only manage six laps.
It was particularly disappointing for the huge numbers of Spanish fans who had turned out to see Fernando Alonso on his return to McLaren.
The two-time world champion was also way off the pace during his brief stint on the track, trailing over 18 seconds behind the time set by Vettel.
Red Bull faired significantly better than 12 months ago as Daniel Ricciardo went fourth fastest in registering 35 laps.
The test in Jerez will be followed by two more in Barcelona later this month ahead of the new season, which starts in Melbourne on 15 March.