Jenson Button believes that he was on target to qualify in the top five for the Monaco Grand Prix before he suffered a fuel pump problem in Q3.
The McLaren driver had shown well during Q1 and Q2 and was confident he could have done far better than ninth on the grid but for having to abandon his second run.
His first run was also affected by the problem, leading Button to describe McLaren as "our own worst enemy."
Asked by AUTOSPORT what might have been possible, Button replied: "P5, but I didn't do the lap so that's just plucking a position of the air, you've got to do the lap to deserve the position and we didn't do that.
"The pace felt good all the way through qualifying in different conditions, in the wet, in the drying conditions and the dry.
"The run in Q3 that I did do when we all went out initially was hurt by the fuel pump problem.
"That got worse through the session so on my last run, I wasn't even getting into seventh gear on the main straight so there was no point continuing."
Button was positive about what the team had achieved during the weekend.
He is certain that the car has improved, adding that it was strong in all the conditions faced in qualifying.
"It's a shame because this weekend, as a team, we have done a great job," he said.
"We have definitely made some improvements.
"We did a great job in tricky conditions in qualifying and we really showed some good pace.
"We felt we could get a lot further up the grid so it is going to be a difficult race tomorrow."
Perez, meanwhile, said seventh was all his McLaren was capable of in qualifying.
"It's a good feeling you maximise the full potential of the car," he said. "I did a fantastic lap and a really strong performance. It's disappointing, though, when you do a good lap and you find you are seventh."