Nico Rosberg and Lewis Hamilton took the front row ahead of Red Bull for today's Spanish Grand Prix, but both men were cautious about their race prospects.
The Mercedes team showed pace throughout qualifying, with Hamilton fastest in the Q1 and Q2 sessions before losing out to Rosberg in Q3.
"It had not been my best weekend up until now," said Hamilton. "I was just a little bit lost as to which way to go and what changes to make, so we left the car the same as it was in practice. My lap was fine, but Nico was just quicker.
"The big concern for the race will be tyre degradation, so it's going to be an interesting one. It will be really good if we can get into the first corner in first and second."
Rosberg made two runs while Hamilton needed only one and thus conserved tyres ahead of what promises to be another hugely tough race on Pirelli's rubber. But after their troubles in Bahrain, Mercedes believe they have made a step forward in using the tyres.
Sebastian Vettel lined up in third place ahead of Kimi Raikkonen's Lotus and the Ferraris of Fernando Alonso and Felipe Massa, all of whom will be quick in the race.
Jenson Button, though, had an embarrassing day. McLaren showed better form – even though new front wings which arrived overnight could not ultimately be used because they could not be scrutineered in time – with Sergio Perez qualifying ninth. But Button failed to get through Q2 and lines up in only 14th place.
"The car felt okay in Q1, but in Q2 I couldn't find the grip for my final run," he said. "It felt as though the tyre pressures may have been too high, but we're not yet quite sure exactly what happened. From 14th on the grid, whatever we do will be difficult."