MONACO, May 23, 2013 (AFP) - Red Bull's once-dominant drivers admitted on Thursday that they are struggling to keep up with 2013 pace-setters Mercedes and Ferrari after being left behind in opening practice for this weekend's Monaco Grand Prix.
Australian Mark Webber, twice a winner on the streets of the Mediterranean principality, wound up fifth fastest behind the leading Mercedes pair led by German Nico Rosberg and Briton Lewis Hamilton.
Vettel was down in ninth and clearly unable to mount a genuine challenge for the front of the grid on Thursday's form.
Asked if he felt he could match Rosberg's speed, Webber snapped: "If we could, we would have done it today...
"One minute and 14.7 seconds round here is not hanging around but let's see how things go. We were not really in the window here last year up until my last lap in Q3, so we need to rediscover that, if I can, and be towards the front.
"And you need to be there, up the front, here..."
Vettel struggled with KERS issues and was unable to find a lap-time boost when he switched from softs to super-softs.
He agreed that one-lap speed was Red Bull's current major weakness.
"Unfortunately we had a big change and we lost quite a lot of time in the afternoon," he said.
"It is not not completely ideal, but that is Friday - or in this case, Thursday...
"We would like to be a little bit more competitive in low-fuel configuration so we need to try and find some lap time there.
"My run on super-soft was very poor, so we need to understand why.
"I wasn't able to improve which you should be able to do quite easily.
"After that I did a long run on super-soft and it seemed quite OK."
Webber added that he was not concerned to be lacking time at this stage as he never expected to be on the pace immediately in Monaco.
"You will never come to Monte Carlo and have the perfect day or perfect set-up," he said.