Red Bull emerged as genuine contenders for pole position in the third practice session for the Hungarian Grand Prix, as Lewis Hamilton racked up vital miles.
World champion Hamilton managed just four laps in FP2 on Saturday, before a side-on crash into the tyre barrier wrecked his ability to collect data.
Rosberg has never finished on the podium at the Hungaroring, but has looked on form this weekend so far, his time of 1:20.261 the quickest of the qualifying simulations.
It was only just the fastest however, Max Verstappen coming in a mere two thousandths of a second down on the German's time.
Mercedes have not won in Hungary since 2013, with Daniel Ricciardo winning in the Red Bull two years ago before Sebastian Vettel's win for Ferrari last season.
The Italian squad were down on race pace against Mercedes on Saturday and once again they look to be short ahead of qualifying - Vettel and Kimi Raikkonen lagging more than half a second off the quickest times.
McLaren again look strong, with Fernando Alonso going seventh fastest after he and Jenson Button were inside the top 10 on Saturday, with Jolyon Palmer a surprise in 10th.
Drivers continued to run wide at turns 4 and 11 - which stewards are looking to clamp down on this weekend.
Laps in qualifying that exceed track limits will be deleted, but drivers have also been warned that punishments will be meted out on raceday.
A note to teams read: "Any driver who is judged to have left the track three times at these corners (when counted cumulatively) will be shown a black and white flag, one further crossing will result in a report being made to the stewards for not having made every reasonable effort to use the track.
"As discussed, this is likely to result in a drive-through penalty for any driver concerned."