Nico Rosberg heads Lewis Hamilton in Japanese GP practice
Nico Rosberg edged title rival Lewis Hamilton by just 0.072 seconds to set the pace in second practice at the Japanese Grand Prix.
The Mercedes drivers, with Rosberg 23 points ahead in their championship battle, were 0.323 seconds quicker than Ferrari's Kimi Raikkonen.
Red Bull's Max Verstappen beat Ferrari's Sebastian Vettel to fourth.
Jenson Button struggled for McLaren, in 16th, eight places and 0.413secs behind team-mate Fernando Alonso.
The 2009 world champion was complaining that the car lacked balance and felt no different from the morning session, when he was unhappy with its feel.
The title battle - and the rain potential
Hamilton has five races left to try to claw back his deficit to Rosberg. He had hoped to start this weekend in the same fashion he conducted the last race in Malaysia, when he was demonstrably faster than Rosberg and was on his way to a comfortable victory until his engine failed late in the race.
Instead, Rosberg was fastest in both sessions, albeit by a small margin in the afternoon as clouds came over Suzuka.
"It's been a really good day with no problems on the car which is great," said Hamilton. "But there's still some work to be done overnight in order to find more pace.
"Hopefully we'll be going into Sunday in good shape."
Rain had been expected overnight and for qualifying but the forecasts are now less confident of that and the weather is uncertain, as it so often is on this eastern coast of Honshu, between mountains and Pacific Ocean.
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- How Friday practice unfolded
Rain would enhance the chances of Red Bull mixing it with Mercedes in qualifying but the race-simulation runs later in the second session suggested that they could keep the world champions honest in the race as well.
Verstappen and team-mate Daniel Ricciardo matched Hamilton's lap-time average on the soft tyres that will be used in at least the first stint of the race.
Ricciardo, winner in Malaysia on Sunday, was only 12th as he did not complete a lap on his qualifying simulation run because it was interrupted for a virtual safety car period after Esteban Gutierrez's Haas stopped on track.
Ferrari's race pace was hard to judge because of off-set tyre choices. Raikkonen's headline lap time, set with a new front wing the team have brought to Japan, suggests they could be in the mix, although the Finn was complaining of a lack of front grip on his race run.
Force India looking quick
Force India looked to be comfortably the fourth quickest team, while Alonso's pace in eighth suggests McLaren should again be able to get at least one car into the top 10.
It was a relatively incident-free session, with no crashes, although Renault's Kevin Magnussen, Williams' Felipe Massa and Sauber's Felipe Nasr all ran wide before rejoining.