Daniel Ricciardo set an impressive pace as he led a Red Bull one-two in second practice at the Singapore Grand Prix, with Mercedes' Lewis Hamilton third.
Ricciardo led team-mate Max Verstappen by 0.556 seconds, with Hamilton a further 0.147secs adrift.
Sebastian Vettel of Ferrari struggled to 11th quickest after aborting one timed lap for traffic and then spinning into the barriers on the second.
His team-mate Kimi Raikkonen was also in trouble and ended up ninth.
Renault driver Nico Hulkenberg was an impressive fifth fastest, behind Hamilton's team-mate Valtteri Bottas, and just ahead of the McLarens of Stoffel Vandoorne and Fernando Alonso on a day McLaren's split from Honda was finally confirmed and it was announced they will use Renault engines next season.
Briton Hamilton goes into this weekend three points ahead of fellow title contender Vettel, on a track where the German and Ferrari are expected to beat their rivals.
I want dominant weekend - Ricciardo
Ricciardo said he had expected a strong performance.
"I knew we'd come here with a good car. I feel prepared, so I'm not surprised with our performance. It's important that we obviously keep that but I have a lot of faith we can stay there all weekend," he said.
"A dominant weekend is what I'm after. I know the challenge tomorrow will potentially be stronger from Ferrari and Mercedes, but I'm confident we can stay there."
Hamilton said Red Bull were "out on their own" and he expected them to still be ahead on Saturday, although the gap might narrow.
"They are just rapid, particularly in the last sector. They also seem to be able to keep temperature out of their tyres for whatever reason," he said.
"We will make some changes to see if we can squeeze some more out of the car but generally we anticipated they would be quick. We thought the Ferraris would be quicker than they are."
- Read: Red Bull to split with Renault at end of 2018 season
- Predict who will top qualifying at Marina Bay
Race simulations: Red Bull could win this
The headline from the day was the stunning performance of the Red Bull, particularly in the hands of Ricciardo.
The Australian was not only half a second clear of the field on the short runs on which teams simulate qualifying, but was also a similar margin ahead on average on the longer race-simulation runs of consecutive laps.
Those long runs gave a clearer picture of Ferrari's competitiveness, with Vettel narrowly slower than Hamilton, who was the next quickest driver after Ricciardo.
Vettel's true pace in qualifying trim was not seen because he had traffic on his first lap and then a half-spin, brushing the barriers, on his second. He did set a couple of fastest-of-all sectors of the lap but did not overall appear to have the pace to challenge Ricciardo.
His fractured session, though, did mean it was difficult to draw any meaningful conclusions about how Hamilton and Vettel might match up over one lap.
"Obviously not ideal I lost the car in the middle sector on my second attempt," said Vettel. "I am not yet happy. I am missing a little bit the balance and then you miss the confidence. We'll see what we can do tomorrow."
The Marina Bay circuit is notorious for the size of the challenge it creates, with a long lap, a bumpy surface and concrete walls around it, all in high temperatures and humidity.
But there were remarkably few incidents, the most serious being Vettel's relatively harmless half-spin into the barriers at Turn 10, from which the car appeared to emerge largely unscathed.
A number of other drivers had moments, Verstappen, Alonso and Haas driver Romain Grosjean all brushing the wall, and the Frenchman also spinning, but all the cars got through the day without major damage.