Lewis Hamilton was fastest in Japanese Grand Prix practice on Friday while Dutch teenager Max Verstappen became the youngest driver ever to take part in a Formula One weekend just three days after his 17th birthday.
Championship leader Hamilton, winner of the last two races, set the pace in a crash-interrupted second session after Mercedes team mate Nico Rosberg had lapped quickest in the morning.
The Briton's time of one minute 35.078 seconds in the afternoon at Suzuka was more than two-tenths of a second faster than Rosberg's best.
Mercedes, who could claim the constructors' championship this weekend if results go their way, were again dominant with their drivers one-two in both sessions.
"It's amazing what this team has done, to be able to come to one of the most demanding circuits for downforce and be that competitive is fantastic," said Hamilton, who leads Rosberg by three points in the standings with five races to go.
"The car didn't feel spectacular this morning, but on the option (tyre) it felt really good."
Finland's Valtteri Bottas kept his Williams at the sharp end of the field, setting the third fastest time in the second session after having gone fourth quickest in the day's opening 90 minutes.
McLaren's Jenson Button, who regards the Japanese Grand Prix as a second home race, followed the Williams by setting the fourth fastest time in his McLaren ahead of reigning world champion Sebastian Vettel's Red Bull.
Kimi Raikkonen led Ferrari's charge in the second session ahead of team-mate Alonso, whose future remained a major talking point after he refused to rule out leaving the sport's glamour team as early as next season.
Alonso appeared to have confirmed the progress the Maranello-based team had made in Singapore, setting the third-fastest time in the morning only to slip back to seventh at the end of the day.
RICCIARDO CRASH
After an uneventful opening session, the challenging high speed figure-of-eight circuit caught several drivers out in the afternoon, with red flags halting the session twice. The threat of rain, with typhoon Phanfone expected to pass south of Suzuka on race day, also hung over practice with a light drizzle falling after a sunny start to the day.
Home hero Kamui Kobayashi crashed less than 10 minutes into the session, his Caterham snapping out from under him to add to the struggling outfit's woes over what has already been a turbulent weekend with bailiffs raiding their British factory.
Red Bull's Daniel Ricciardo also ended his session in the barriers, with the Australian spearing off the road just as he was rounding the corner leading onto the home straight.
"I made a mistake," said the ever-smiling Australian. "The tyres probably cooled too much and out of the last chicane I got on the power and had a few moments and just couldn't catch it."
Ricciardo, the only man other than the Mercedes duo to have won a race so far this year, had been fastest at the time of his accident and, despite having completed only three laps, ended the day 10th quickest.
"They (Mercedes) were really quick today," Ricciardo said. "Maybe the race will change. Right now in the dry, all going well, we can still be third on the grid."
Toro Rosso's Jean-Eric Vergne was 11th. Reliability issues sidelined him after just two laps early in the session but the Frenchman eventually completed 17 laps before stopping again.
The Frenchman had sat out the morning session to hand his car to Verstappen, son of former F1 driver Jos, who acquitted himself well with the 12th quickest time. The Dutch youngster was only four tenths of a second shy of 20-year-old Russian Daniil Kvyat in the other Toro Rosso. He completed 22 laps in total before engine trouble brought a smoky end to his outing with seven minutes remaining.
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