The F1 world - and a very crowded media centre - got its first look at the new Mercedes car on Monday morning, as the winter testing ban ended and Valencia burst into life.
The Mercedes' MGP W01 is an evolution of the title-winning 2009 Brawn, but also clearly different, with an unique V-shape to the nose for better underneath air flow.
Gary Paffett headed the early timesheets in McLaren's new MP4-25, before Felipe Massa set the best lap on the Ferrari F10's track debut.
After two hours of running, the new Sauber (Pedro de la Rosa), Renault (Robert Kubica) and Williams (Rubens Barrichello) came next in the pecking order, followed by Buemi.
"Williams are not launching as such, when the car rolls out at 10am, that will be its debut," said spokeswoman Claire Williams.
Rosberg's first laps in the W01, watched on by his father and 1982 world champion Keke, were not representative of Mercedes' likely form this year.
The 24-year-old German, who posed with the car in the morning with Michael Schumacher, has swapped the blue on his regular helmet colours for silver.