Rosberg and Mercedes fire ominous warning on day two

Mercedes finally hit the front in 2015 pre-season testing on Friday, as Nico Rosberg set an imperious new benchmark on day two in Barcelona.
Elsewhere there was encouragement for McLaren, as Jenson Button completed more than 100 laps on the team's most successful day to date, and Force India, who rolled out their new car for the first time and clocked up close to 80 laps across the afternoon.
But it was Mercedes who stole the show. Despite being the early favourites given their dominance in 2014, the Silver Arrows had not troubled the top of the timesheets over the opening nine days of testing. That changed, however, as the team bolted on Pirelli's soft compound for the first time this year, allowing Rosberg to clock a blistering 1m 22.792s on his first run.
The German came close to bettering that on subsequent runs, but it was ultimately good enough to keep him comfortably top, more than a second clear of the field - and more than 2.5s faster than Lewis Hamilton's 2014 pole time at the Circuit de Barcelona-Catalunya.
Williams locked out second in Mercedes' wake courtesy of Valtteri Bottas, who took over from day-one pacesetter Felipe Massa, with Sauber's Felipe Nasr fractions of a second down the road in third.
Ferrari's Sebastian Vettel was fourth, albeit 2.5s off Rosberg's pace, while Button earned McLaren fifth place, a welcome boost to add to their lap tally.
Lotus's Pastor Maldonado shaded Toro Rosso's Max Verstappen and Red Bull's Daniil Kvyat for eighth, with Nico Hulkenberg rounding out the day's runners in ninth for Force India.
Verstappen was one of the day's busiest men with 139 laps, although his running was cut slightly short by an electrical problem on the STR10.
Button also hit issues late on when he stopped out on track between Turns 7 and 8, bringing out the red flags for only the second time of the day. Kvyat had prompted the first stoppage when he was instructed to halt out on track as a precaution after Red Bull discovered a hydraulic sensor issue.
For more pictures from Barcelona, see our testing gallery.
Unofficial Friday testing times from Barcelona to follow...

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