Kimi Raikkonen set the pace ahead of team-mate Sebastian Vettel in Friday practice for the Formula One Chinese Grand Prix as the Ferrari pair dislodged the dominant Mercedes duo.
Finn Raikkonen, a former winner for Ferrari in China, jumped to the top of the order with a one minute 36.896 second lap in the second session, beating German team mate Vettel by 0.109 seconds.
Ferrari were tipped pre-season to challenge Mercedes' two-year dominance and the Italian team desperately need a trouble-free weekend if they are two live up to that promise after suffering reliability issues in the season's opening two races.
Raikkonen and Vettel initially appeared to be struggling, with the Finn in particular repeatedly complaining over the radio about his car's handling.
But the duo turned the tables on their German rivals in the afternoon with their runs on the fastest, red-walled, super-soft compound tyre, making that session just the second time this season that a Mercedes has not finished at the top.
"It's been quite a tricky day," Raikkonen said.
"I don't know if it's the conditions or the wind or something but I was sliding a lot and obviously not feeling very nice.
"Once we put the supersoft tyres on we have more grip from the tyres and that helps. For whatever reason we've been quite struggling apart from the supersoft tyre."
Championship leader Nico Rosberg was third for Mercedes, 0.237 seconds off Raikkonen's benchmark.
Team mate and world champion Lewis Hamilton, who heads into Saturday's qualifying session with a five-place grid penalty for a change of gearbox, was fourth, 0.433 seconds adrift.
Rosberg had set the fastest time ahead of Hamilton in Friday morning's interrupted opening session and Mercedes head into qualifying and the race as favourites, despite Ferrari's session-topping efforts.
The German team have won 34 of the last 40 races and started the last eight on pole.
Rosberg, who leads the standings by 17 points from Hamilton, heads into Sunday's race gunning for his sixth straight win, while the Briton is aiming to complete a hat-trick of Chinese Grand Prix victories.
Hamilton, who has the most wins of anyone in China, however will have his work cut out as the highest he can start the race from is sixth.
Red Bull's Daniel Ricciardo ended the day fifth, the Australian, fourth in the morning, setting a time 1.247 seconds adrift.
McLaren driver Fernando Alonso, cleared by doctors to compete in Sunday's race after a final round of medical tests following the morning session, was 11th.
The Spaniard, forced to miss the last race in Bahrain due to injuries sustained in an accident last month in Australia, completed 42 laps over the entire day.