Mercedes has revealed that Nico Rosberg's poor start at Suzuka was due to an engine issue.
Though he was neck and neck with teammate Lewis Hamilton down the straight into the first corner, in addition to the Briton having the better line for the next turn, the German was suffering a power deficit.
Forced wide by Hamilton, Rosberg was to subsequently lose positions to Sebastian Vettel and Valtteri Bottas, though by the end of the afternoon he was back in second again.
"The initial getaway was good for both cars," said Toto Wolff, according to Motorsport.com. "Nico had a little bit of an issue with a hotter power unit and when it kicked in after a couple of seconds, he didn't have same power as Lewis.
"It was showing up on the formation lap," he admitted. "I haven't got an explanation yet but there was definitely a slight drop in power due to a temperature related issue. We don't know yet if it was down to the driver, but it affected him the whole race – and definitely affected him in the fight at Turn 1 and Turn 2."
In reaction to claims that the German should have mounted a more robust defence of his lead, Wolff said: "I don't think it has anything to do with being soft or not; it is always very difficult to race your team-mate. We have seen great racing afterwards with Bottas, and it was a tricky situation for both.
"Lewis said he had understeer in the car and he ran out of track. Two cars side-by-side through Turn 2 is difficult anyway," he added.