Brazilian Felipe Massa celebrated his first Formula One pole position since 2008 as Williams stunned leaders Mercedes on Saturday (local time) and swept the front row of the Austrian Grand Prix starting grid.
Finland's Valtteri Bottas qualified in second place for the Mercedes-powered former champions with championship leader Nico Rosberg only third fastest for the Mercedes factory team.
It was the first time this season that Mercedes had failed to take pole and Sunday's race will be Williams's first start from the front of the grid since Venezuelan Pastor Maldonado in Spain in 2012.
"Williams are back to the top, they are back to fight. I am pleased for me and the team as well," declared an emotional Massa whose last pole was with Ferrari at his home grand prix before finishing that season as runner-up.
"After a long time I hope this is just the beginning of great possibilities. I hope to be in this position again," added the Brazilian who suffered near-fatal head injuries in a freak accident in Hungary in 2009.
Britain's Lewis Hamilton, Rosberg's team mate and closest championship rival who is 22 points behind the German after seven races, had a nightmare session.
The 2008 world champion will have to fight back from ninth place after his first flying lap of the revamped Red Bull Ring was disallowed because he exceeded track limits and he then spun on his final attempt.
"It was just two not very good laps. Or one-and-a-quarter-laps - I didn't finish my second one," he told the BBC. "My first lap was looking good and I went wide in the second to last corner - I think that lap would have done it.
"We're going to be strong tomorrow, it's going to be very, very hard from where we are, but of course I'll do everything I can to try and get some good points for the team. It's damage limitation I guess."
Red Bull's quadruple world champion Sebastian Vettel fared even worse, qualifying 13th at a home circuit for the team.
"I'm not happy, let's put it that way," said the German, who will move up a place because Force India's Mexican Sergio Perez drops five from 11th for causing a collision at the previous race in Montreal.
"I think anything is possible tomorrow but surely we are not as quick as we'd like to be."
Australian team mate Daniel Ricciardo, winner of the race in Canada, qualified ahead of Vettel yet again and will start fifth with Ferrari's Fernando Alonso fourth.
Denmark's Kevin Magnussen qualified sixth for McLaren while Russian newcomer Daniil Kvyat starts seventh for Red Bull's sister team Toro Rosso.
Both rookies have experience of racing at the Red Bull Ring from junior series last season, something most of their established Formula One rivals lack.
The last time two Williams drivers lined up together on the front row was in Germany 11 years ago - the year Austria was last on the calendar - and qualifying was a great turnaround for the family-run outfit.
Last season, Williams scored only five points and finished ninth overall but this year they have already bagged 58 and are threatening to overtake fifth-placed McLaren.
"I am so happy with what has happened today, with us, our team, it was such a great moment. It is a long time since I last had a pole position," Massa told reporters.
Bottas also celebrated his best ever qualifying performance.
"It's a great result for the team. We've made progress throughout the year and now we get this result. The hard work is all paying off," said the Finn.
"It will be a different story tomorrow I think. We have a big, big job to keep the Mercedes cars behind us - and some of the other cars - Ferrari and Red Bull - can do well also."
Rosberg, who had qualified on pole for the last three races, sounded relaxed.
"I still think we are the quickest team and car at the moment," said the German. "It is more difficult than starting on the front row, of course, but I think it is possible to overtake on this track."
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