Nico Rosberg heads Lewis Hamilton in Japanese GP practice
Nico Rosberg headed team-mate and title rival Lewis Hamilton in first practice at the Japanese Grand Prix as Mercedes left the rest far behind.
Rosberg was 0.215 seconds quicker than Hamilton, who complained of a lack of power early in the session.
Hamilton is 23 points behind with five races and a maximum of 125 points still available and needs to beat Rosberg this weekend to revive his title hopes.
Ferrari's Sebastian Vettel was 1.094 seconds behind Rosberg in third.
Mercedes have said they are running their engines in a revised spec, which effectively means a minor loss of performance at certain points of the weekend, following Hamilton's engine failure while leading in Malaysia last weekend.
Ferrari's Kimi Raikkonen was fourth fastest, ahead of the two Red Bulls of Daniel Ricciardo and Max Verstappen, who used the slower medium tyre to set their times rather than the soft.
The Force Indias of Nico Hulkenberg and Sergio Perez were next, ahead of the McLaren of Fernando Alonso, who was four places and 0.674secs quicker than team-mate Jenson Button despite going off and damaging his car at Spoon Curve.
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Alonso was able to get back to the pits and take a full part in the session.
Button was complaining about the balance over the radio, saying: "We've got a lot of work to do."
Haas' Romain Grosjean was the only other driver to crash at arguably Formula 1's best and most demanding track, although Verstappen also ran wide at Spoon.
The Frenchman lost control at the notorious Degner Two corner, where he slid wide and damaged his front wing against the barrier, although he, too, was able to get back to the pits.
The session was run in warm, humid weather, which is expected to continue throughout Friday before rain arrives overnight and could well affect qualifying on Saturday.