Nico Rosberg heads Lewis Hamilton in Japan practice
Nico Rosberg beat Mercedes team-mate and title rival Lewis Hamilton to set the fastest time in first practice at the Japanese Grand Prix.
Max Verstappen became F1's youngest driver at 17 when he did a solid job on his debut before his engine failed.
Rosberg, who is three points behind Hamilton in the championship, was 0.151 seconds quicker than this team-mate.
Hamilton was on a quicker lap when he ran wide at the tricky Degner Two corner.
Dutchman Verstappen, who was driving in first practice in place of Jean-Eric Vergne as the team prepare him for his race debut in 2015, was 0.443secs slower than team-mate Daniil Kvyat.
The son of former F1 driver Jos Verstappen ended up 12th fastest, two places behind Kvyat.
Verstappen is to drive in the first practice sessions at three of the four remaining races after Japan, missing only next weekend's event in Russia, when he has a race in the European Formula 3 series.
His session ended when he was forced to pull off in the Esses with seven minutes remaining with smoke pouring from the rear of the car after what appeared to be a problem in the power unit.
BBC F1 analyst Allan McNish said: "He was very clean and tidy. To be 0.4secs from Daniil Kvyat is very solid - even though Kvyat has not been here before he has had a season of racing behind him."
At the front of the field, the Mercedes drivers were in a league of their own as they embarked on the latest chapter of their intense title fight.
Rosberg was 0.311secs quicker than Hamilton on the first runs, with Hamilton edging closer on the second set of fast laps before the two began to focus on preparation for Sunday's race with laps on a heavier fuel load.
Hamilton has turned a 29-point deficit into a small advantage with two wins in the last two races, aided by Rosberg's retirement in Singapore.
McNish said: "Clearly there has been a momentum that has gone in Hamilton's favour in the last two races and Rosberg has to stop that.
"It's only 0.1secs between them - that's the sort of margin we have seen all year."
Ferrari's Fernando Alonso was third fastest. The Spaniard's future with Ferrari is in doubt after he refused on Thursday to rule out not driving for another team within the next two years.
He was 0.576secs slower than Rosberg and a similar margin ahead of the Williams of Valtteri Bottas in fourth.
Ferrari's Kimi Raikkonen was fifth fastest, but 1.15secs slower than his team-mate, and ahead of the McLarens and Red Bulls.
McLaren's Kevin Magnussen was sixth, split from team-mate Jenson Button by Red Bull's Daniel Ricciardo, with world champion Sebastian Vettel ninth.
As ever, there were a number of incidents on the demanding Japanese track, where the narrow circuit and limited run-off areas tend to punish mistakes.
Caterham reserve driver Roberto Merhi spun at Spoon Curve early in the session and was very nearly collected by Bottas.
Shortly afterwards, Sauber's Esteban Gutierrez ran off the track and into the gravel trap at the difficult Degner One corner, while both Hamilton and Sebastian Vettel ran over the kerb at the Degner Two corner but rejoined with no damage.