Mark Webber beat his Red Bull team-mate Sebastian Vettel for the first time this season to grab pole position for the Spanish Grand Prix.
The Australian headed the German, who was on pole for all the season's first four races, by 0.2 seconds as the Red Bulls were in a league of their own.
The McLarens of Lewis Hamilton and Jenson Button were third and fifth, split by Ferrari's Fernando Alonso.
Renault's Vitaly Petrov was sixth, ahead of Mercedes's Nico Rosberg.
Webber's first pole since the Belgian Grand Prix last August is an important landmark after being dominated by his team-mate so far this season.
BBC F1 commentator Martin Brundle said: "Webber psychologically scores a direct hit on Sebastian Vettel. It should be a fascinating duel between the Red Bull drivers. Can Lewis Hamilton, like last year, hang on and give them a hard time?"
Webber is already 38 points behind Vettel in the championship, so a win on a track at which he dominated in 2010 would be an important boost for his already dwindling title hopes.
Some of the shine was taken off his performance by the knowledge that Vettel was not able to use his Kers power-boost system in the second and final parts of qualifying, depriving him of potentially 0.2secs a lap.
But Webber probably would have been on pole anyway and Vettel graciously refused to blame his Kers problems for failing to take his fifth consecutive pole this season.
"It's not right to say Mark is on pole because I didn't have Kers," he said. "Mark did a better job today.
"I'm not concerned, we are working hard on the Kers, and I think we will be on top of it in the race."
Webber added: "It was a good session. We thought he had an advantage and that we would probably battle for pole, not to underestimate the other guys. I was obviously praying my number went to number one on the gantry when I crossed the line and it did. Today was my day."
Webber was nearly a second faster than Hamilton, but the Englishman will have hopes of pushing the Red Bulls in the race, as he has been able to do several times this season.
"I'm happy with the result," Hamilton said.
"I'm pushing like crazy, as you can tell. I made some changes going into qualifying, and it was the wrong choice. It's good to be in P3, but it was massively close to the guys behind, and nowhere near as fast as the guys in front.
"We're not as quick as the Red Bulls, but nonetheless we'll push as hard as we can. I'm starting on the clean side, and the aim is to get to P1 in turn one!"
Perhaps the lap of the session was from Alonso. Ferrari had looked to be struggling for pace throughout practice and the first two parts of qualifying.
He was 0.8secs slower than the McLarens in the second session but Alonso pulled some pace from somewhere in the final session and failed to snatch third from Hamilton by only a few thousandths of a second.
He was helped by Hamilton locking a wheel on his qualifying lap. Nevertheless, Alonso's race engineer Andrea Stella said over the radio: "That was a special lap." A thrilled Alonso, who broke a run of qualifying fifth for every race this season, whooped in response.
Afterwards, the Spaniard said: "I did a perfect lap. I reckon that if I tried to repeat it 20 times I could not do better. When you do a lap like that it's hard to put into words what one feels: always being on the limit in every corner is a special feeling."
Kers has proved something of an Achilles' heel for Red Bull this season - only at the Turkish Grand Prix have the team had a completely trouble-free weekend.
If Red Bull can run at their own pace - which appears vastly superior to their rivals - that should not be a problem.
Their main concern will be getting beaten down to the first corner of the race by Hamilton or Alonso, which could turn the grand prix on its head.
That possibility is heightened by Vettel starting on the dirty side of the grid, where there is less grip than on the racing line.
Button said he was pleased with his qualifying lap.
"I'm three hundredths [of a second] off third, and the positive thing is I'm starting from the clean side of the grid. It's difficult to predict what will happen, but tyre-wise in particular I think we're in pretty good shape."
There were impressive performances from Petrov and, particularly, Williams's Pastor Maldonado, who shrugged off a difficult start to his grand prix career by getting into the top 10 qualifying shoot-out for the first time and make ninth spot on the grid, behind Ferrari's Felipe Massa.
Rosberg's team-mate Michael Schumacher qualified 10th after opting not to use the faster soft tyres in final qualifying so he has an extra new set for the race, a potential advantage.
The veteran was 0.1secs slower than Rosberg in the second part of qualifying.
Schumacher explained: "We had a problem with Kers and we couldn't go out for another qualifying lap so we preferred to save the tyres for tomorrow.
"We went for soft tyres in Q1. I'm pretty sure Kers will work tomorrow and DRS so hopefully there will be some overtaking opportunities. We'll have some fun."
Force India drivers Paul di Resta and Adrian Sutil did not use soft tyres in qualifying and were slowest in the second session, lining up 16th and 17th.
BBC F1 co-commentator David Coulthard said: "That's clearly sacrificing grid position so they can use more soft tyres in the race. A very interesting tactic."
Their decision meant Lotus driver Heikki Kovalainen was able to qualify ahead of them in 15th place, the team's best qualifying position in the dry since they entered F1 at the beginning of last year.
Kovalainen said: "We wanted to go for the qualifying time and maximise our performance. Everybody on the pit wall agreed, and I think it was the right choice."
BBC F1 chief analyst Eddie Jordan said he felt that was playing "too short a game", to which Kovalainen responded: "That's the boring approach."
Two big names missed the cut in the first part of qualifying.
One was Renault's Nick Heidfeld, whose mechanics were not able to repair his car in time after a huge fire in morning practice.
"The fire was the biggest one I've had in F1," said Heidfeld. "I still hope for a good race and with fresh tyres you can still move forward and fight."
More surprising was the failure of Williams driver Rubens Barrichello, who was afflicted by a gearbox problem and was unable to use the soft tyres he needed to be quick enough to make the cut.
"We had a gearbox problem. The car was not doing very well when I was running and when I came back they said I couldn't go out again.
"It's very frustrating because the car is not fast and it is not running often either, so it's a bit of a mess right now."