McLaren's Lewis Hamilton said the Formula 1 season was wide open after he was beaten to pole position by Red Bull's Sebastian Vettel in Bahrain.
Vettel had not qualified higher than fifth in the three previous races, and Mercedes' Nico Rosberg, who was on pole in China a week ago, was only fifth.
"The way the season's shaping out it's anyone's at the moment," Hamilton said.
Hamilton said he was expecting a tough race against Vettel and his team-mate Mark Webber, who qualified third.
"I've always thought the Red Bulls were the quickest on race pace," said Hamilton. "They were just struggling a little in qualifying - all of a sudden they've picked it up.
"I thought they would eventually catch up, they've generally got a bit more downforce than anyone else, as they have [had] the last few years.
"I don't know where they've picked up their time, but they've obviously made a big difference. Perhaps in other races it's been a [lack of] tyre temperatures and here in the hotter conditions it's easier for them."
Hamilton added that he was "less than 0.1 seconds away [from Vettel] and that is a real positive for me".
He said a good start would be key, although his chances of doing that are lower than Vettel's, as Hamilton - and team-mate Jenson Button - are on the side of the grid that has less grip because it is off the racing line.
"The start is going to be key," he said. "Each year [in Bahrain] I have started on the dirty side, and here I am again.
"But we have much better launches this year so fingers crossed I'll be able to challenge them down into Turn One."
Hamilton's team-mate Jenson Button will start directly behind him in fourth place on the grid, with Mercedes driver Nico Rosberg - who was on pole by 0.5 seconds in China a week ago - only fifth.
"It definitely makes the race more fun," Button said. "I'm looking forward to it.
"We were expecting the Red Bulls to be very quick in qualifying, so to be close to them is good, and one surprise is to be in front of Nico.
"It's weird, isn't it, F1 at the moment? It's exciting but difficult to understand."