Champion-in-waiting Sebastian Vettel made only his third mistake of an exemplary season as Jenson Button topped both practice sessions ahead of Sunday's Japanese Grand Prix.
Vettel's error occurred as the clock ticked down on the 90 minutes for the opening session at the Suzuka circuit. Running wide at Degner One, Vettel was left with nowhere to go as he ground to a halt at Degner Two, nudging the nose of his Red Bull gently against a tyre barrier.
Button, who this week remained loyal to McLaren by signing a multi-year contract, set the fastest times at the end of both 90-minute sessions.
After leading a one-two with team-mate Lewis Hamilton in the first session, Button stayed out in front in the second, shaving just under two seconds off his earlier best time.
The 31-year-old set a lap of one minute 31.901secs for the 5.807km circuit, but unlike in the first session there was no Hamilton in close attendance as his fellow Briton had to settle for eighth.
Instead, it was Ferrari's Fernando Alonso who was his closest challenger, with the Spaniard 0.174secs adrift. Vettel, who needs only a point from the race to claim back-to-back titles, was third, 0.194secs down.
Vettel's mistake at the end of FP1 was followed up in the second session by other incidents, the most notable of which saw Rubens Barrichello crumple his Williams into a tyre barrier. The veteran Brazilian completely lost his line going into Degner One, running wide onto the grass on the approach.
With no grip, Barrichello was then spun round, his car hurtling backwards across the gravel before slamming into the tyres.
In what turned out to be a wretched session for Williams, Pastor Maldonado suffered a mechanical gremlin that forced him to pull off the track at Degner One 10 minutes after Barrichello's accident.