While McLaren left the Nuerburgring empty-handed on Sunday, their hopes blowing up along with Kimi Raikkonen's Mercedes engine, Williams shone.
Ralf Schumacher's triumph after 15 months and 23 races without a win, leading Colombian Juan Pablo Montoya in a one-two finish, sealed a memorable weekend for Williams and BMW after announcing a renewed partnership to the end of 2009.
"It shows that we have closed the gap and we are in the fight for the championship," said BMW motorsport director Mario Theissen.
"Ralf drove a perfect race," added BMW's Gerhard Berger. "He showed everyone that he can win a race and is capable of being a world champion."
It was their second win in three Grands Prix, Montoya winning in Monaco, and left Ferrari with 95 points, Williams on 82 and McLaren 76.
"I think the team has done a fantastic job. The last four races, since Austria, we have been very quick," said Montoya, whose race collision with world champion Michael Schumacher threw Raikkonen a lifeline.
It also kept the championship bubbling, even if Ferrari increased their lead in both standings. Ferrari's Schumacher now leads the Finn by seven points. Ralf is 15 adrift.
BALL ROLLING
"In Austria I was leading until I blew up, then Monaco we won. The last race we were very strong, finished second and third, and now first and second," said Montoya.
"It looks as if we can probably keep the ball rolling
The next race is in France on Sunday, allowing the teams no chance to draw breath, and Montoya was on pole there last year with Ralf fastest the year before.
Both sensed the tide turning their way, with McLaren struggling to get their new car ready to race and the Williams FW25 making noticeable progress.
"Everything has improved," said Theissen. "The whole team has worked very hard in the last few months, especially the aero team.
"We are not finished making improvements. I'm confident there will be more improvements in the second half of the season."
Ralf will fancy his chances in France, even though Michael has won six times there, including last year when he collected his fifth world championship at Magny-Cours.
That extraordinary season seems like ancient history now. The Nuerburgring, with Schumacher spinning off and finishing fifth, was the first time this year that Ferrari had not looked capable of winning.
But both expect France to be better.
"It is a racetrack where we went well in the last couple of years or even more," said Barrichello, now the only driver from the top three teams yet to win this year.
Raikkonen, who led Sunday's race until his engine blew, nearly won in France last year while team mate David Coulthard, who crashed out on Sunday while fifth, won in 2000.
"The gap to Michael can easily be closed with a good result and that is what we want to achieve next weekend," said Coulthard, whose own title hopes are slim.