Lewis Hamilton was in convincing form as he headed Mercedes team-mate Nico Rosberg in second practice at the Malaysian Grand Prix.
The world champion was 0.223 seconds quicker than the German, with Ferrari's Sebastian Vettel 0.661secs off in third ahead of team-mate Kimi Raikkonen.
Red Bull's Max Verstappen was fifth fastest ahead of Force India's Sergio Perez and McLaren's Fernando Alonso.
The day began with a dramatic pit fire involving Renault's Kevin Magnussen.
A leaking fuel breather pipe forced the Dane to jump quickly out of his car after just two laps of the first practice session, and it took repeated attempts to extinguish the fire as fuel continued to escape while the team frantically tried to empty the full tank.
Magnussen was unhurt and the car was repaired in time for him to take part in the second session, in which he was 19th fastest but incurred the wrath of McLaren's Jenson Button for blocking the 2009 world champion on his fastest lap.
The was no such trouble for Hamilton, who enjoyed a welcome and needed return to form after a poor last race.
Hamilton finished third in Singapore two weeks ago as Rosberg won, losing the championship lead for the first time since taking it in July and dropping eight points behind Rosberg with six races to go heading into this weekend on the demanding Sepang track.
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After an inconclusive first practice session that was hard to read, the Briton was on impressive form in second practice.
As well as being fastest on the qualifying simulation runs on the softest tyre, Hamilton also set the pace throughout the first part of the session, by 0.399secs despite using the hard tyre while Rosberg was on the medium.
Behind the Mercedes, Ferrari seemed to have an edge on Red Bull as the two teams continue their battle to end the season second in the championship - Vettel was 0.432secs quicker than Verstappen.
Alonso's position in seventh place was a surprise fillip for McLaren.
The Spaniard was using an upgraded Honda power-unit, with a lighter block and redesigned exhaust, aimed at improving the car's qualifying performance.
The development is aimed at Honda's home race in Japan next weekend but has been introduced in Malaysia because taking it means a 30-place grid penalty for Alonso for using too many engine parts.
The plan at this stage is to revert to an older-spec engine for the rest of this weekend.
Button, who will not have the new engine until the US Grand Prix in two races time at the earliest because Honda does not want grid penalties at Suzuka, was 10th fastest.
Magnussen was playing catch-up after losing the entire first session and ended up seven places and 0.7secs slower than team-mate Jolyon Palmer.