Jenson Button described McLaren's Bahrain Grand Prix as "disastrous" as he failed to finish and Lewis Hamilton lost the championship lead.
Button suffered a differential failure when heading for fifth place while Hamilton ended up eighth after delays in two consecutive pit stops.
"It was a pretty disastrous day," said Button. "I don't understand why we were so far off the pace."
Hamilton said: "I guess this was just one of those days."
The race was won by Red Bull's Sebastian Vettel, who leapfrogged from fifth in the championship to first, four points ahead of Hamilton.
Button is fourth behind Vettel's team-mate Mark Webber, and 10 points adrift of the German.
Button said: "We just don't have the pace here. One or one and a half seconds - we don't understand where that's gone.
"The last few races whether we've won or not we've had good pace, but not here."
Team boss Martin Whitmarsh said: "We weren't quick enough, we've made mistakes and we had a failure on Jenson's car, so it was a pretty bad day in the office.
"We were killing the rear tyres and killing them very quickly. Our drivers didn't stand a chance.
"It's a bit of a concern, we have to be calm, analytical and it's something we have to accept.
"We've come back from these things plenty of times before, we have bad days and this was certainly one of them."
He added: "We have to focus on what we did wrong and clearly we've done something wrong.
"You look at our pace today by comparison to our long runs on Friday, we were a second slower than we were.
"These tyres are very challenging and if you get in the sweet spot you are in great shape. If you get out of it you're in for a tough time and we had a very tough time this afternoon."
Hamilton was running in third place until his first pit stops, but his race was hampered by problems fitting his left-rear tyre at his first two pit stops.
It was the same wheel on which Button had had a similar problem in China a week ago.
Hamilton said: "By rights, we should have been fighting to finish in the top four today, but it didn't work out like that in the end.
"We lost a bit of world championship momentum today but on the plus side we still picked up four points and every point is valuable in a season as close fought as this one."
Whitmarsh said: "Any guy who volunteers to be a (wheel) gun man is a brave guy.
"I have been speaking to him just now because I know how hard he is being on himself. He's taken it very badly. I was giving him the support and reassurance of the team.
"All of us make mistakes from time to time and we are probably harder on ourselves than others are.
"I'm very protective of them because they deserve my protection. They try hard they know the pressure they're under.
"We have to look at the process, the equipment and the approach."