Formula One championship leader Jenson Button's title hopes received a significant boost today when a Paris appeal court ruled the Briton's controversial Brawn GP car was legal.
The International Automobile Federation (FIA)'s court of appeal also cleared Toyota and Williams, whose cars use similar 'double-decker' or 'split-level' rear diffusers and which rivals had claimed broke the spirit of the rules.
Button won the first two races of the season in Australia and Malaysia after overcoming protests from struggling champions Ferrari, Renault, Red Bull and BMW-Sauber.
The four teams had then appealed against the stewards' decisions.
The FIA said in a statement that the court, which met on Tuesday, had decided "to deny the appeals submitted".
"Based on the arguments heard and evidence before it, the Court has concluded that the Stewards were correct to find that the cars in question comply with the applicable regulations," the statement added.
It said full reasons would be provided later.
Button and Brazilian team mate Rubens Barrichello will now be favourites to complete a hat-trick of Brawn victories in Sunday's Chinese Grand Prix in Shanghai.
"We respect the right of our competitors to query any design or concept used on our cars through the channels available to them," Brawn principal Ross Brawn said in a statement.
"The FIA technical department, the stewards at the Australian and Malaysian Grands Prix and now five judges at the international court of appeal have confirmed our belief that our cars have always strictly complied with the 2009 technical regulations."
Had the verdict gone against the three teams, Button could have been stripped of his wins with the championship thrown into turmoil.
Instead, rival teams will now be racing to come up with their own versions of the diffuser, which ensures a smooth flow of air under the car to create more downforce, at a time when testing is banned.
Renault have already said they have a prototype that could be used in China.
"This decision will have an enormous impact on the championship," Ferrari's 2007 world champion Kimi Raikkonen, whose team have yet to score a point, said on his website (http://www.kimiraikkonen.com) earlier in the week.
Renault's double world champion Fernando Alonso warned last month that Brawn could run away with the championship if given the all-clear.
"If the diffusers are legal, the Brawns are going to be nearly unreachable for any other team," the Spaniard said after the Australian Grand Prix.
Formula One has undergone major change this season with radically revised aerodynamic rules leading to grey areas in interpretation.
Brawn have taken over the Honda team operation, with the Japanese manufacturer pumping hundreds of millions of dollars and more than a year of effort into their new car before deciding to pull out in December.
Toyota, currently second in the constructors' championship behind Brawn after finishing on the podium in both races, said they had never doubted their car was legal.
"We studied the technical regulations in precise detail, consulting the FIA in our process, and never doubted our car complied with them," team principal Tadashi Yamashina said in a statement.