Jenson Button showed he will make Sebastian Vettel sweat for his second world Formula One championship after the Briton topped the timesheets in both practice sessions at the Japanese Grand Prix.
The 31-year-old McLaren driver, after leading morning practice, set his benchmark time of 1 minute 31.901 seconds in the 90-minute afternoon session at a sunny but windy Suzuka.
Button, the 2009 world champion, is 124 points adrift of Red Bull's Vettel, meaning he has to win all five remaining races - and needs Vettel to finish no better than 11th in every race - to deny the German back-to-back titles.
Vettel, who crashed out in the final stages of the morning session, was third in afternoon practice, 0.194 seconds off top spot.
He needs only one point to seal the world driver's crown.
Vettel, 24, says the crash was a timely reminder to retain focus.
Splitting the only two men in mathematical contention for the title was Spaniard Fernando Alonso, who finished 0.174 seconds behind Button's session-best time for Ferrari.
Australian Mark Webber was fourth for Red Bull, while Alonso's Ferrari teammate, Brazilian Felipe Massa, was fifth.
German pair and Mercedes team-mates Michael Schumacher and Nico Rosberg were sixth and seventh ahead of Briton Lewis Hamilton, who finished a disappointing 1.344 seconds behind team-mate Button for McLaren.
Russian Vitaly Petrov (Renault) and Swiss Sebastien Buemi (Toro Rosso) rounded out the top 10.