Nico Rosberg edged out Mercedes team-mate Lewis Hamilton to set the pace in final practice at the Malaysian Grand Prix.
Rosberg was 0.184 seconds clear of the world champion and half a second ahead of the two Ferraris of Kimi Raikkonen and Sebastian Vettel.
Williams drivers Felipe Massa and Valtteri Bottas were next ahead of Red Bull's Daniel Ricciardo.
McLaren-Honda's Fernando Alonso and Jenson Button were 15th and 18th.
But McLaren continued their improved form from a poor first race - Alonso was 2.3 seconds off the pace, halving the gap between McLaren and Mercedes in just two weeks.
Button was 0.321secs behind Alonso, the two McLarens split by Force India's Sergio Perez and Sauber's Felipe Nasr.
Friday practice had suggested Ferrari might challenge Mercedes, but the world champions were always likely to have something in hand, and so it proved in sweltering conditions during the early afternoon in equatorial Sepang.
With the track temperatures at more than 60C, drivers, cars and tyres were tested to the limit, and as so often happens Mercedes stretched their legs as the important part of the weekend neared.
|Andrew Benson on Sepang's extreme temperature|
|"Situated just north of the equator, and pretty much at sea level, the heat, accompanied by high humidity, is all-pervading.|
|It envelopes you, permeates you, overwhelms you. And for the drivers, it takes on a different dimension again.|
|Strapped inside a carbon-fibre cockpit wearing four-layer fireproof overalls, underwear, balaclava and helmet, subject to extreme physical demands in an environment that quickly takes on the track temperature - which was 60C or so on Friday and promises to be the same again today - and controlling what is effectively a ground-hugging missile. It defies belief."|
Rosberg, who had a clean day on Friday, was on top from the moment he took to the track, while Hamilton, badly affected by reliability problems on Friday, was again struggling a little.
Hamilton set the fastest time on Friday despite doing only a handful of laps because of engine and telemetry problems and went into Saturday having had no chance to do any set-up work.
It showed in practice as he complained of the car's braking being "all over the place", and wrestled with the car as he had a couple of out-of-control moments.
Hamilton was more than 0.5secs behind Rosberg on the hard tyre in the first part of the session, but managed to more than halve that deficit on the qualifying simulation runs on the medium tyre later on.
Ferrari appear to have a slight edge on Williams in the battle for best of the rest, but Raikkonen and Vettel - separated by only 0.021secs - were just over 0.1secs quicker than the evenly-matched Williams pair.
Ricciardo may also have a chance of joining that fight after improvements to Red Bull's Renault engine following a difficult opening race to the season.
He was nearly 0.2secs off the Williams, but did his qualifying run much earlier in the session, when conditions were slightly slower.
Red Bull were again pushed by their low-budget junior team Toro Rosso - Carlos Sainz Jr was only one place and 0.011secs behind Ricciardo.
The Spaniard's team-mate Max Verstappen was ninth but 0.388secs slower.
Sauber's Marcus Ericsson completed the top 10, ahead of the Lotus drivers Romain Grosjean and Pastor Maldonado, the second Red Bull of Daniil Kvyat, Force India's Nico Hulkenberg and Alonso.