With track temperatures soaring, Hamilton set a sizzling pace with a quickest lap of one minute 18.
341 seconds in the afternoon session.
Formula One world championship leader Rosberg, who had been fastest before lunch with a best of 1:19.131, was second on the timesheets a mere 0.024 off Hamilton’s pace.
Dominant Mercedes, seeking their first German Grand Prix victory as a works team since Argentine Juan Manuel Fangio triumphed 60 years ago at the Nuerburgring, finished one-two in both sessions.
Friday was the first chance to assess the performance of cars since the governing body ruled against a front and rear interconnected suspension (FRIC) system.
All teams had presented their cars for scrutineering without the systems on Thursday but the times showed no seismic change in the pecking order even if champions Red Bull appeared to have edged slightly closer.
“It was quite difficult to find the balance with the track being so hot and it is a tricky circuit to drive in general,” said Hamilton.
“The car is a bit different now as everyone made some setup changes in a different direction to what we’ve had in the past, but it’s still fun to drive.”
Mercedes also made a rare pitlane bungle when they had the wrong tyres ready for Hamilton during a race simulation and Rosberg had to wait behind him with overheating brakes.
“We had a bit of a situation in the pit lane when my team mate came in suddenly just before I was called in too,” said the German. “But the boys reacted quickly and cooled my car and brought his tyres out.”
Ferrari’s Fernando Alonso, who has won the last two races at the southern circuit which alternates with the Nuerburgring, was third fastest in the morning – and 0.292 off the pace – and then ninth in the afternoon.
“I don’t think going away with FRIC changed much in terms ofdriving style…but running without it, we just have to adapt and be as well prepared as possible with what we have,” said the Spaniard.
Red Bull’s Daniel Ricciardo, the only driver other than the Mercedes pair to win a race this season, was fourth and third fastest respectively.
The Australian’s quadruple champion team mate and last year’s German GP winner Sebastian Vettel was sixth and eighth.
Further back, Susie Wolff had a second chance to make her mark among the men after her involvement at Silverstone two weeks ago was cut short due to an engine problem with the Williams.
The first woman to take part in a grand prix weekend in 22 years managed 22 laps in the morning session and ended up an impressive 15th fastest, only a fraction slower than the Force India of 14th placed Mexican Sergio Perez.
Perez had made headlines in Britain when he jokingly told a Spanish television reporter that he would not want to be beaten by a woman driver. His time on Friday of 1:20.598 compared to Wolff’s 1:20.769.
Brazilian Felipe Massa, the team’s race regular, was only 11th fastest with a best time of 1:20.542 but was sixth after lunch with team mate Valtteri Bottas taking back his car from Wolff and ending 10th quickest.
Wolff’s session was not without stress, and she hit trouble on her opening lap out of the garage when the car suffered a sensor problem.
Whether she gets a chance to progress further remains uncertain and Wolff was under no illusions.
“The next step is obviously to do more and that’s the difficult part, to get more opportunities,” she said.
“I was incredibly lucky to get the chance with this team this season and of course I have to try to get more opportunities, but as we know that’s not easy. So I need to start fighting for that now.”
Caterham, under new ownership following the departure of Malaysian entrepreneur Tony Fernandes, had a torrid day with Kamui Kobayashi’s car catching fire. The Japanese joined marshals in extinguishing the flames.
(Editing by John O’Brien/Tony Goodson)