Valtteri Bottas laid down a new marker by clocking the fastest time of Formula One's 2017 pre-season testing in Barcelona on Wednesday.
Mercedes endured a low-key Tuesday and both Lewis Hamilton and Bottas had spoken of the threat posed by Ferrari to their dominance of the sport for the upcoming season.
But Bottas, who had the best time of the first week of testing last week, rocketed to the top of the timesheets with a one minute 19.310 seconds at the Circuit de Catalyuna - four tenths faster than his effort last week - during Wednesday's first session.
The Finn - Mercedes' replacement for world champion Nico Rosberg in 2017 - produced the time over two-and-a-half hours into the session, and also racked up the most laps with 70.
Felipe Massa enjoyed a fine Tuesday by setting the pace for Williams and once again impressed, registering a time just 0.110secs shy of his former team-mate.
Ferrari had their first minor blip of testing when Kimi Raikkonen needed a two-hour stop in the garage as the Italian team carried out a "fluid system check", but he still posted the third quickest time despite being restricted to 39 laps.
Max Verstappen also made improvements in his Red Bull, the exciting teenager clocking his fastest time of testing in one minute and 20.516secs.