Valtteri Bottas was quickest Friday in practice before the Japanese Grand Prix locked down ahead of an approaching super typhoon, finishing a tenth of a second ahead of teammate and world championship leader Lewis Hamilton.
The Mercedes pair, benefiting in Japan from an aerodynamic upgrade package to their W10 cars, were comfortably ahead of the third-fastest Red Bull of Max Verstappen in the second session of the condensed racing weekend at Suzuka.
The Ferraris of Charles Leclerc and Sebastian Vettel, who had dominated practice and qualifying at the previous four grands prix since the summer break, could only trail in fourth and fifth after failing to record a clean lap on the fastest soft tyres.
Just before the first session began on Friday morning, race organisers announced that the entire Saturday track programme, including qualifying, had been scrapped for safety reasons in the face of the approaching Super Typhoon Hagibis.
Qualifying was rescheduled to 10am (0100 GMT) Sunday, with the race still taking place at 2:10pm (7:10 CAT) as originally planned, providing the weather improves.
The loss of Saturday's timetable added extra spice with only Friday's two practice sessions available to prepare the cars for qualifying.
And should bad weather linger on Sunday morning and prevent the qualifying session taking place, the governing body FIA confirmed that the timings from Friday's second practice will be used to determine the starting grid.
That would leave Mercedes sitting pretty with a front-row lockout as they look to secure the one-two finish they need to clinch a record sixth successive constructors championship.
Finland's Bottas recovered from a mid-session spin on the final bend to lap the 5.807-kilometre circuit in 1min 27.8785sec, 0.100sec ahead of Britain's Hamilton.
Verstappen of the Netherlands was third on 1:28.066 in his Red Bull, 0.281sec slower than Bottas, with Monaco's Leclerc was fourth on 1:28.141 and Vettel fifth on 1:28.376.
It was a timely riposte by Mercedes to the resurgent Ferrari team who had dominated practice and qualifying since the summer break.
A win for Hamilton on Sunday would leave only Bottas, who lies 73 points behind, able to catch him in the drivers' standings with just four races to come after Japan.
It would also put the Englishman in line to wrap up a sixth drivers' title, a feat only previously achieved by Michael Schumacher, and third world title in a row at Mexico later this month.
The fanatical Japanese spectators, left reeling from the news of a blank Saturday, were given something to cheer on Friday morning as local hero Naoki Yamamoto made his Formula One debut, replacing Pierre Gasly in the Toro Rosso for the practice session.
"He actually apologised to me for being in my car," said Gasly, who was back in the car in the afternoon's second free practice recorded the ninth fastest time.
"I said to him to enjoy and make sure you enjoy every single lap. He's a really good guy, really fast, really talented," added the Frenchman of the 31-year-old reigning champion in Japan's Super Formula and Super GT series.
The thousands of spectators lining the circuit had plenty of chance to see their hero as he completed 30 laps -- more than any other driver -- and finished 17th fastest in the session.