Sebastian Vettel headed Mark Webber in a Red Bull one-two in Friday practice at the Japanese Grand Prix.
Vettel, who had been third behind the two Mercedes cars in the first session, outpaced Webber by 0.168 seconds.
Mercedes' Nico Rosberg was third fastest, 0.262secs off Vettel, and ahead of Lotus's Kimi Raikkonen and Romain Grosjean.
Mercedes' Lewis Hamilton was sixth and Ferrari's Fernando Alonso 10th after a spin at the Degner corners.
Minutes before the end of the second session, it emerged that former Marussia test driver Maria de Villota had been found dead in her hotel room in Seville.
Suzuka lived up to its reputation as one of the most difficult tracks in the world, catching out even the best drivers, with Vettel, Alonso, Hamilton and Raikkonen all having moments of varying severity.
"The balance is decent," said Vettel. "I think we can still improve the car, especially looking after the tyres, which will be crucial for the race.
"It's tricky. We've seen a lot of drivers struggling, it's a difficult track."
Alonso, who must finish eighth or better on Sunday if Vettel wins to prevent the German from winning the title, promised on Thursday that he would "attack" for the rest of the season now his title hopes were all but over and he had an uncharacteristically messy day.
He ran wide at both the Hairpin and Spoon Curve in the first session and then had a spin on his first flying lap on the faster 'medium' tyre, ensuring he did not set a representative time and ended the session 0.389secs slower than team-mate Felipe Massa.
It was a sobering day for Alonso, for a glance at the times suggests that finishing eighth may not be that easy.
That is the position where Massa ended up - behind the Red Bulls, the Mercedes, the Lotuses and the surprise Toro Rosso of Daniel Ricciardo.
Alonso's struggles appeared to confirm the impression that Ferrari have slipped backwards in the last few races.
Hamilton and Vettel joined Alonso in having incidents.
The Englishman got his Mercedes on to the exit kerb at Degner Two but rescued the car, while Lotus's Romain Grosjean had a very similar moment a few minutes later.
And Vettel had a brief off-track excursion at Spoon Curve before rejoining.
Others were not so lucky.
Raikkonen got in his medium tyre qualifying simulation run but then spun in the middle of the fast Dunlop Curve and beached the car in the gravel during his race-simulation run.
Both McLaren's Sergio Perez and Williams's Pastor Maldonado crashed early in the session, and missed out on both their qualifying and race-simulation runs.
Maldonado lost his car at the tricky Degner Two corner, where Marussia's Jules Bianchi and Caterham's Giedo van der Garde had both crashed in the first session.
Perez then spun at the entry to Spoon Curve after letting his outside wheels stray partially off the track as he turned in at about 120mph.
The McLaren hit the barrier heavily side-on but Perez, who is under pressure because he has still not had his contract renewed for next season, was unhurt.
"On the entry I put a wheel on the asphalt and I lost the back end," said Perez. "There is not much room so I went straight into the wall."
McLaren managing director Jonathan Neale said "internal discussions" were still taking place over Perez's future, but confirmed that Button, who was ninth, was under contract.