The Mercedes Formula 1 team was caught out by the extent of the cooling issues its drivers suffered in the Austrian Grand Prix, according to team boss Toto Wolff.
Nico Rosberg and Lewis Hamilton overhauled the Williamses of Valtteri Bottas and Felipe Massa to finish one-two at the Red Bull Ring, but both were compromised by similar ERS and brake cooling issues to the ones that spoiled their Canadian GP earlier this month.
Hamilton was warned several times about his brake temperatures, while Rosberg made a point of repeatedly ducking out of Sergio Perez's slipstream in the middle portion of the race to keep his own Mercedes healthy.
Wolff said his team was surprised by the extent of the issues.
"Coming one and two was so hard today," Wolff said.
"We experienced things we didn't expect - again some little things on the cooling side.
"We struggled with the brakes again today - there are not long enough straights to cool them down, and it was much hotter today so it came as a bit of a surprise to us actually.
"Williams was doing really well - I don't think they had the same problems, so it was a tough one today."
Wolff also praised his team for the job it did in managing the issues to get both cars successfully to the end of the race.
"That was the achievement of the race - lots of engineers on the power unit side and the car side were managing the car," Wolff added.
"We always maintained the spirit of having equal settings on both cars, but after Montreal we needed to make sure we were managing all the critical parts in the right way.
"You don't want to manage your pace between your drivers if you have a risk of losing the race, and this was a bit of a struggle [in the early stages].
"The last third was probably the least stressful because we knew we had the gap to Bottas and it was just a matter of maintaining all important parameters on the car within the right operating window."