Red Bull will be tough to beat - Button
Brawn's Jenson Button admitted Red Bull's performance had caught him by surprise in qualifying for the Chinese Grand Prix.
The Red Bull pair of Sebastian Vettel and Mark Webber will start first and third, while championship leader Button is back in fifth.
"It is not as good as I expected, but the Red Bulls are really competitive here," he said.
"We didn't think they were quite that competitive. They'll be tough to beat."
Button, who took pole in the first two races of the season, was also out-qualified by team-mate Rubens Barrichello for the first time this season.
The Brawn cars are thought to be carrying a heavier fuel load than Red Bull's - cars in the top 10 run-off are not allowed to refuel between qualifying and race.
But Button was more concerned by Red Bull's performance in the second qualifying session, when all cars run light on fuel.
"It looked like they had about three-tenths of a second on us in Q2," he said.
"It is a pity we're starting behind them because it is tough to overtake here, but we will see."
Vettel's pole is Red Bull's first and team boss Christian Horner admitted they had executed an "aggressive strategy" in qualifying.
"It paid off," he added. "Obviously, it's the best place to be starting the race, but I think managing the tyres will be crucial in the race.
"The Brawn is still very, very quick. We don't know where they're going on strategy. I'm sure when the fuel loads come out, we'll get a clear indication."
Mark Webber was denied a place alongside team-mate Vettel only by Fernando Alonso's sensational display in his revamped Renault.
"I was expecting the session to be a bit tighter," said the Australian.
"We'll see how the fuel loads go tomorrow, but we've done a very good job.
"Q2 was strong and the car's behaving very well with a lot of grip."
There will be an exclusive interview with Jenson Button on BBC1 in the build-up to the race, with live coverage beginning at 0700 BST