Sergio Perez has labelled Red Bull's dramatic double retirement at the Bahrain Grand Prix as a "low day" for the team.
Reigning world champion Max Verstappen looked on course to finish second behind Ferrari's Charles Leclerc after losing out in a pulsating mid-race battle, only for his car to fail him in the closing stages of the opening race of the season.
That promoted Carlos Sainz into second and Perez into third, only for the Mexican to suffer a seemingly similar problem on the final lap of the race.
Asked what the issue was that caused his retirement, the Mexican explained: "We think it is the fuel pump and at the hairpin on the final lap, it locked completely at the rear.
"I knew it was going to be close to get it to the line because the issue was coming progressively lap by lap and we thought we could have got it to the end but unfortunately, we didn't."
There are further concerns for Red Bull's powertrains department, which enters its first year in F1 after taking on Honda's IP, with Pierre Gasly's AlphaTauri ending the race in flames.
On the mood in the camp after the failures, Perez added: "It is very frustrating. It is a very low day for our team.
"It is a difficult start to the new year but the positive is we are quick, we just have to figure out, make sure we are more reliable, understand the issues and we have got some pace to find to get closer to the Ferraris."