Max Verstappen will become F1 world champion for the second time if he wins Sunday's race and takes the point for fastest lapGeorge Russell said he had "no idea" of the competitive order at the first Japanese Grand Prix in three years after topping a wet Friday practice.
The Briton headed team-mate Lewis Hamilton to a Mercedes one-two on the first day of F1 running at Suzuka since 2019 as a result of the pandemic.
Russell was 0.235 seconds quicker than Hamilton, with Max Verstappen's Red Bull 0.851secs off the pace in third.
Dry weather is forecast for qualifying and showers for Sunday's race.
Russell and Hamilton both used a fresh set of intermediate tyres to set their fastest times in the driest part of the second session, while Verstappen did not.
Russell said: "It's probably not going to be that representative for this weekend but definitely good learning for the future.
"There is a chance for Sunday it could be wet but it looks dry tomorrow. It's nice to top the time sheets and definitely made some improvements from P1 because we were at the bottom of the time sheets then.
"I think we will be fighting for the top six as always. I hope we can have a shot at something better but I truly don't know. Have to wait until FP3. That will be a crucial session for everybody."
Mercedes struggled in the first session, which was also wet, but Hamilton said they had managed to get their tyres up to temperature in the second - a problem the world champions have been struggling with all season.
Hamilton said he had "no clue" where Mercedes were in competitiveness.
"I have no idea," he said. "If it's dry I imagine the Ferraris and Red Bulls will be quite quick. I hope we will be fast but that's a hope that continues at every race weekend."
Verstappen will clinch his second world title at Suzuka on Sunday if he wins the race with fastest lap, regardless of the results of Ferrari's Charles Leclerc and Red Bull's Sergio Perez, the only two other drivers still in with a mathematical chance of the championship.
He can still do so in other circumstances, but then it would depend on the results of Leclerc and Perez, who are 104 and 106 points behind him with a maximum of 138 still available.
Verstappen said: "I would have liked that it was a little more representative. It wasn't a complete disaster with the weather, we could at least get round and do a little bit of stuff. But in terms of knowing where you are with pace in the wet it is a bit tricky.
"I'm looking forward to tomorrow to see where we can be in the dry. It's starting from zero tomorrow in the dry and I don't think it will make massive differences throughout the grid."
Perez, winner in Singapore last weekend, was fourth fastest, just 0.048secs behind his team-mate.
Ferrari's Carlos Sainz was fifth from Kevin Magnussen's Haas, who did a new-tyre run late in the session to vault up the time sheets, and and Alpine's Fernando Alonso, who was fastest in the first session.
Leclerc, the fastest man over one lap on balance this season, was down in 11th place after a troubled session complaining of problems with his left front wheel.
There were no major incidents in the second session, after the first ended with Mick Schumacher's Haas in the wall.
The German, who is fighting for his future in F1 in the face of claims that Haas are likely to sign the veteran Nico Hulkenberg to replace him in 2023, lost control after the chequered flag on his return to the pits following a practice start.
Schumacher was unable to take part in the second session after Haas decided to change his chassis as a precaution following the incident.
