Mercedes F1 boss Toto Wolff says the German outfit's massive tyre and pitstop blunder in Sunday's Sakhir GP was caused by a radio failure in the team.
Mercedes looked on course for a routine 1-2 in Bahrain, albeit with George Russel leading a sensational charge.
The Black Arrows duo negotiated the first round of pit stops without any issues but a safety car on lap 59 compelled the Brackley squad to double stack its drivers for a second tyre swap.
Alas a communication failure led to Russell being fitted tyres from Bottas' allocation which in turn forced the crews to refit on the Finn's car his older tyres.
"It was a colossal fuck up," admitted a candid Wolff. "What happened is that when we called the pit crews out, they get a call on the radios and bring the right tyres out.
"One side of the garage, George's side, didn't hear the pit call. We had a radio that didn't function, and then the wrong guys with the wrong tyres came out."
Russell was forced to pit again one lap later so the team could fit the designated set of tyres.
"We knew immediately when Valtteri didn't have his tyres, we knew that Valtteri's tyres were on George's car," Wolff said.
"We fitted Valtteri's old hard tyre that we just took off to the car again, and we knew we needed to pit George again."
Russell took off with the bit between his teeth and positioned fifth in the running order. Spurred on by race engineer Peter Bonnington, the young Briton picked off his rivals one by one after the restart to move up to second behind Perez with 15 laps to go.
But an ominous call over the radio informed Russel that a slow puncture was developing. The subsequent pitstop unfortunately killed Mercedes and Russell's hopes of a remarkable maiden win for the driver of the day.
"The slow puncture probably came from him having to run off the line so many times in order to overtake," said Wolff.
"As for the race win? I don't know. I think our planner said he would catch up to Sergio and maybe DRS would have helped us, but I'm not sure [if he would have won].
"Sergio drove a brilliant, brilliant race, and deserves the race win because we made too many mistakes, and were unlucky with the puncture."