Rosberg topped both FP1 and FP2 and even broke the unofficial lap record around the Spielberg venue with a 1:07.373 flyer in the morning, leaving his title rival 0.357s adrift.
The gap shrunk down to just 0.019s in the rain-hit afternoon session but that was only after the current championship leader aborted his final hot lap, which was set to be much faster.
“It was a decent start to the weekend but Lewis didn’t get his laps together so he didn’t show what he could do,” Rosberg said.
“It is a pleasure to drive on this track since they made the new asphalt and the new kerbs, there is a lot of grip out there so we are really going fast. We broke the lap record today and we were much faster than last year I think, so it is a great feeling.
“It is smooth out there too, it used to be really bumpy. Apart from that, on one lap we seem quick, surprisingly quick maybe, we thought others would be close and it didn’t seem like it, but these are early days.”
Despite Mercedes' early advantage, Rosberg believes that some factors, like tyre management on the ultrasoft compound and weather conditions, could end shuffling the deck this weekend.
“For the long run it was difficult with the rain, we couldn’t rally practice the long runs for the race so we might have to do it on Saturday morning.
“The shortest lap of the year is here so traffic is always an issue [in qualifying], and it is forecast to start raining at the end of qualifying so let’s see when that comes.
“We are starting the race with the ultra-softs and they seem way too soft for this track. On one lap they are great but after that they disintegrate very quickly so that will be a huge challenge in the race if they fall apart quickly, it could mix things up.”