Mercedes underlined their superiority in the new Formula One season as first Lewis Hamilton and then Nico Rosberg led the timings in the Malaysian Grand Prix practice sessions on Friday.
Hamilton topped the first session with his team-mate third, and it was Rosberg, winner of the season-opener in Australia, who took control in the later run-out.
Both drivers carried the message, "#TributeToMH370", on their cars as Malaysia mourns 239 people presumed dead in a disappeared passenger jet. Sunday's race will be preceded by a minute's silence.
"It was crazy conditions out there. In the very, very warm temperatures, it's a huge challenge to get everything right," said championship leader Rosberg.
"The cars are on the edge and the tyre degradation was higher than expected today -- we are sliding a bit more this year, perhaps because of the reduced downforce levels.
"The quickest teams seem to be closer together than in Australia, so we still have work to do overnight to improve our level of performance."
While Friday practice has little bearing on the race weekend, Mercedes will be pleased to have extended the dominance they showed in Australia -- although it was tight at the top in the second session.
Rosberg's time of 1 min 39.909 was three hundredths ahead of Ferrari's Kimi Raikkonen, with world champion Sebastian Vettel improving to within six hundredths for third spot. The top 11 drivers were all within one second of each other.
Hamilton, who veered off the track in both outings, was fourth in the second session ahead of Ferrari's Fernando Alonso, Williams' Felipe Massa, Red Bull's Daniel Ricciardo and Jenson Button of McLaren.
"The car feels good and our focus was on trying to understand the tyres and make sure the balance is right for the weekend," said Hamilton, the 2008 world champion.
"There are areas where we can improve so we're keeping focused on our own work, rather than being distracted by what the others are doing."
Lotus's Pastor Maldonado and Caterham's Kamui Kobayashi both sat out the second session for repairs as their dismal start to the season continued.
And Lotus had another setback when Romain Grosjean had to pit early for repairs before returning late on -- when he suffered another problem with his gears and had to retire.
Jean-Eric Vergne span and Nico Hulkenberg, who went fastest early in the second session, ran wide into the gravel as handling problems persisted with this year's new Formula One cars.
"It's really not handling well," grumbled Denmark's Kevin Magnussen, classified second for McLaren in his debut F1 race two weeks ago, while Raikkonen later complained, "My rear tyres are sliding around".
Rosberg hit the front about a third of the way into the 90-minute run and he was later joined by Hamilton at the top of the timesheets as Mercedes showed their superior adaptation to this year's wide technical changes.
But Raikkonen then divided the team-mates as he went second, and Vettel also timed quicker than Hamilton as the Red Bull of the four-time world champion showed encouraging signs after an early retirement in Melbourne.
Ricciardo is fighting his disqualification from second in Melbourne over fuel irregularities, and his session ended when he ran wide and took an extended trip through the trackside gravel and grass.
Shortly after the second session, dark clouds shrouded the track and thunder rumbled overhead, an ominous sign for a race which has been repeatedly hit by heavy rain.