Nico Rosberg continued Mercedes' run at the top of the timesheets in Bahrain, posting a 1:33.283 on Saturday for the week's fastest time.
Replacing team-mate Lewis Hamilton on the final day of the second pre-season test, Rosberg set a blistering pace in the morning while doing short runs.
The last of those proved to be the quickest with the Mercedes driver crossing the line with a 1:33.283, which was almost a full second up on the week's previous best set by Hamilton on Friday.
However, it wasn't all smooth sailing as Rosberg also brought out the red flags in the morning session. Merc, though, said that wasn't an issue with the car but rather Rosberg just stalled it and he was back out just a few minutes later. He stopped again late in the afternoon.
Second place went to Jenson Button although his best time 1.674s off the pace.
Kimi Raikkonen was third for Ferrari but was a further two seconds off the P1 time. He also caused a late red when he crashed at Turn 4 bringing the session to an end.
New Williams test driver Felipe Nasr was fourth fastest ahead of Pastor Maldonado. The Lotus driver, who stopped in the afternoon session, posted a best time of 1:38.707.
Sergio Perez, another to bring out the red flags, finished sixth quickest despite his day being curtailed with a drive-train issue. He completed only 19 laps with a best time of 1:39.258.
Daniel Ricciardo was seventh on yet another day to forget for Red Bull. He completed just 15 laps and did not run in the final three hours of the test.
His 1:39.837 put him ahead of Toro Rosso's Jean-Eric Vergne while behind them on the timesheets there were other teams with serious problems.
Kamui Kobayashi was only able to venture out in the final hour of play after team-mate Marcus Ericsson had problems in the morning which resulted in a smokey end to his running.
Meanwhile, Marussia completed five laps the entire day due to "component reliability issues" while Sauber told Autosport that "there was a problem with an interior part of the monocoque." That meant a chassis change and just seven laps for Adrian Sutil, who was responsible for a red flag in the final hour.
01 Nico Rosberg Mercedes 1:33.283 89 laps
02 Jenson Button McLaren-Mercedes 1:34.957 +1.674 66 laps
03 Kimi Raikkonen Ferrari 1:36.718 +3.435 82 laps
04 Felipe Nasr Williams-Mercedes 1:37.569 +4.286 87 laps
05 Pastor Maldonado Lotus-Renault 1:38.707 +5.424 59 laps
06 Sergio Perez Force India-Mercedes 1:39.258 +5.975 19 laps
07 Daniel Ricciardo Red Bull-Renault 1:39.837 +6.554 15 laps
08 Jean-Eric Vergne Toro Rosso-Renault 1:40.472 +7.189 19 laps
09 Kamui Kobayashi Caterham-Renault 1:43.027 +9.744 17 laps
10 Marcus Ericsson Caterham-Renault 1:45.094 +11.811 4 laps
11 Jules Bianchi Marussia-Ferrari no time 5 laps
12 Adrian Sutil Sauber-Ferrari no time 7 laps
Day Four's Action In Bahrain