Sebastian Vettel headed a Ferrari one-two in final practice at the Chinese Grand Prix as Mercedes struggled.
Lewis Hamilton had a scrappy session, featuring a number of errors including a huge 540-degree spin, and was fifth, a second off the pace of his title rival.
Mercedes team-mate Valtteri Bottas was third, but 0.743 seconds off Vettel. Red Bull’s Max Verstappen was fourth.
Daniel Ricciardo suffered a major engine failure in his Red Bull.
Ricciardo’s Renault engine failed in a cloud of flame and smoke, and Red Bull face a race against time to get the car ready for qualifying at 07:00 BST.
And the failure means Red Bull are heading rapidly towards engine penalties this season.
It is only the third race of the season and Ricciardo has already had to change to his second of the only two permitted energy stores for the season. The failure in practice will mean he has to take a second of the only three permitted internal combustion engines.
If a driver has to use more than the allowed number of engine components, it means an automatic grid penalty.
It was a strange session, with a slight distortion of the competitive order that had been established in the first two races, perhaps because of low track temperatures in the cool weather in Shanghai.
Hamilton, in particular was struggling. The world champion ran wide at a number of corners before a trip onto the artificial grass on the exit of Turn 10 caused a massive spin, as the car rotated one and a half times. He went back out, but was unable to get within a second of Vettel.
Bottas, too, was struggling. The Finn was faster than Hamilton but his best time was set on the soft tyre – he failed to improve on the ultra-soft, which ought to be the quickest.
Kevin Magnussen’s Haas was sixth quickest, about where the team is now expected to be after a strong start to the season, but the Force Indias of Sergio Perez and Esteban Ocon were seventh and eighth just a day after technical director Andrew Green explained that the car had a fundamental imbalance issue.
And Sergey Sirotkin gave Williams some good news. The team were slowest of all in Bahrain a week ago, but the Russian rookie was 10th quickest, splitting the Renaults of Carlos Sainz and Nico Hulkenberg.
McLaren again look to be struggling – a week after failing to get a car into the final top 10 qualifying shoot-out led to an “emergency debrief”, Fernando Alonso and Stoffel Vandoorne were 12th and 13th in China.
Their only solace was that they were quicker than the Toro Rosso cars, which use the Honda engine McLaren rejected at the end of last season on the basis that it was the only thing stopping them competing close to the front.