Mercedes has revealed Nico Rosberg was down on power compared to team-mate Lewis Hamilton in the first two corners of the Japanese Grand Prix after his power unit overheated slightly.

Hamilton passed Rosberg in the first two corners after getting a better start from second on the grid. He made the move stick in the second corner as Rosberg had to take to the exit kerb and fell down the order to fourth.

"The initial get away was good for both cars but Nico had a little issue with a hotter power unit and when it kicked in after a couple of seconds, he didn't have the same power as Lewis," Mercedes boss Toto Wolff explained. "This is temperature related. There was a slight drop in power due to a temperature related issue. We don't know if it is down to the driver. It affected him from turn one and two." Wolff admitted Hamilton had to nurse the car at times in the race due to reliability fears.

"Lewis was managing the gap. For us that wasn't visible because the cars weren't shown, but we had some minor drama with the car, temperature related issues. Lewis flat-spotted his tyre and that caused massive vibration - when we took the tyre off the car it was flat-spotted, so that could have ended badly. We tweaked the power unit and the chassis a lot because we were seeing signs of reliability issues, which worried us a bit."

But Wolff had no problems with the way his drivers battled in the first two corners.

"I don't think it has anything to do with being soft or not, it is very difficult to race against your team-mate. We have seen some great overtaking afterwards against Bottas. It was a tricky situation for both because Lewis had understeer in the car and he ran out of track and two cars side by side through turn two is difficult anyway."