Renault, winners in Melbourne for the last two years with Michelin, scored just four points in a race won by Ferrari's Kimi Raikkonen ahead of Renault's former champion Fernando Alonso in a McLaren.
All the teams are using Bridgestone tyres this season after Michelin decided to pull out a year before the official switch to a single supplier.
"We know we are behind, we knew this from the beginning," Briatore told reporters.
"We have a problem because the moment we put the Bridgestone on the 2006 car, immediately McLaren was quicker than us. Our car was so well-balanced with the Michelin, really we lost more than anybody," he added.
"The performance today really was a little bit worse than what we expected."
The loss of double champion Alonso has also been a blow, the Spaniard winning seven races last season before moving to McLaren.
Italian Giancarlo Fisichella, winner in Melbourne in 2005, was fifth on Sunday, while Finnish rookie Heikki Kovalainen had a dismal afternoon and ended up 10th.
Alonso was runner-up to Ferrari's Kimi Raikkonen at Albert Park, with McLaren team mate Lewis Hamilton on the podium in the British rookie's debut race. Germany's Nick Heidfeld was fourth for BMW Sauber.
Renault could be thankful that Ferrari's Felipe Massa started at the back of the grid due to a gearbox failure in qualifying and subsequent engine change. The Brazilian, who would otherwise have undoubtedly been challenging Raikkonen at the front, finished sixth.
"I did think we could outrace BMW and we didn't outrace BMW," said Renault's engineering head Pat Symonds, who felt the gap between his team and Ferrari was about as expected while that with McLaren and BMW was greater.
"The fact that we've got a better picture now of the relative competitiveness doesn't really alter the way we go about things," added Symonds.
"This time last year we were out in front but we were still working pretty hard to make sure that we stayed there.
"The important thing is to try and analyse where we can best put the limited resources that you always have to try and close that gap down, and that's really where the analysis will be going on this week.
"We have three days of testing in Malaysia before the next race, there are a few new bits coming as always, so we're working from there."
The next race is at Sepang on April 8.
