Mercedes fired a warning shot at their rivals in Spain on Friday as Nico Rosberg's very first timed lap on the soft tyres saw him destroy the competition.
Up until Friday's running, the third last day of pre-season test, Mercedes had focused mainly on developing their W06 and working on reliability.
That changed on Friday afternoon when, for the first time during winter testing, a set of soft tyres was bolted to Rosberg's Mercedes. And what a difference it made.
The German, runner up in last year's Championship, crossed the line with a 1:22.792 to edge Valtteri Bottas by 1.203. The Finn's time, a 1:23.995, was also set on the soft tyres.
Felipe Nasr, who was quickest at lunch, dropped to third place ahead of the Ferrari of Sebastian Vettel. The latter was 2.547s down.
Jenson Button had a much improved day compared to Thursday. On the opening day of the final test he amassed just seven laps whereas on Day Two he covered over 100 with a best time of 1:25.590.
It was undoubtedly McLaren-Honda's best day of the pre-season but did end with a red flag as the MP4-30 stopped out on track at Turn 7 just 20 minutes before the close of play.
Pastor Maldonado, who caused the day's final red flag when his E23 stopped at the pit entry with a minute on the clock, was sixth quickest ahead of Max Verstappen, who had an early shower due to an "electrical problem."
But, as Toro Rosso pointed out, the Dutch rookie was "still smiling though, he's happy with his 139 laps."
Daniil Kvyat brought his RB11 home in eighth place having once again caused a stoppage.
Bringing out the red flags in the afternoon's session, the first of the day's three, Red Bull reported that it was a "pre-cautionary stop on track to check a hydraulic sensor issue."
Meanwhile, Nico Hulkenberg in the newly-launched Force India VJM08 completed the timesheets.
His best time for the day was a 1:28.412 but, more importantly, he managed 77 laps on the car's debut.
01 Nico Rosberg Mercedes 1:22.792 106 laps
02 Valtteri Bottas Williams 1:23.995 1.203 90 laps
03 Felipe Nasr Sauber 1:24.071 1.279 141 laps
04 Sebastian Vettel Ferrari 1:25.339 2.547 143 laps
05 Jenson Button McLaren 1:25.590 2.798 101 laps
06 Pastor Maldonado Lotus 1:26.705 3.913 140 laps
07 Max Verstappen Toro Rosso 1:26.766 3.974 139 laps
08 Daniil Kvyat Red Bull 1:26.965 4.173 84 laps
09 Nico Hulkenberg Force India 1:28.412 5.620 77 laps