Britain's Jenson Button says McLaren still need to search for pace despite topping the timesheets in both practice sessions at the Japanese Grand Prix on Friday.
Button is the only driver who can deny German Sebastian Vettel a second world title this weekend at Suzuka, and would need to win
Sunday's 53-lap race -- and have Vettel not finish in the top 10 -- to keep the title race alive with races in South Korea, India, Abu Dhabi and Brazil to finish the season.
While Button was pleased with his performance on Friday, the 2009 world champion still feels Red Bull hold the edge heading into Saturday's qualifying session.
Red Bull team-mates Vettel and Mark Webber have shared all 14 pole positions so far this season between them although Button suggested McLaren had the potential to challenge the runaway leaders in the constructors' championship this weekend.
"I'm pretty happy with today, but we need to improve a lot more to really feel confident that we could really challenge the Red Bulls," Button said.
"There's a few areas where we're a little bit weak that we have to improve in terms of balance, but hopefully we can find that overnight.
"I don't think we're the quickest still -- on long runs, we still have a bit of work to do to challenge the Red Bulls -- but we have a good base."
Button feels Red Bull and particularly Vettel still hold the edge with heavy fuel in the cars.
"They were extremely quick, and I don't think we were that slow with heavy fuel loads. I think Ferrari are probably running more fuel today than they normally do because they had a shock in the race in Singapore, but we'll just get on with our own work," said Button.
Button has never won in Japan, but says the 5.807-kilometre Suzuka layout offers one of the greatest challenges for the drivers.
"Practice and qualifying is hard enough, but when there's 24 cars out there, it's madness -- but good madness," he said.
"A lot of people had offs today, and ran wide into the gravel and made mistakes. It's not very forgiving here, and it's very tricky because of that.
"It's good in a way, and we like that sort of circuit. I don't mean that it's dangerous, but when you go off (here) you go into the gravel and not onto asphalt, which makes it fun for us to drive around.
"You're driving around here by the seat of your pants."
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