The Mercedes pairing were among many to explore the track limits frequently as the drivers adjusted to life without the FRIC suspension systems that all teams have removed in advance of the weekend.
Sebastian Vettel was fastest on 1m20.295s in the busy first half-hour of session as several drivers made use of the extra set of soft tyres that have to be handed back to Pirelli at the 30-minute mark.
At that point Mercedes finally showed its hand as first Rosberg, then Hamilton, went half a second faster than their rivals, a gap only Alonso could partially bridge - and then only with a committed lap.
Hamilton was quickest of all in the first two sectors, but could not unite the two over the course of one lap, finishing on 1m19.196s to Rosberg's 1m19.131s.
Ferrari used the early part of the session to evaluate aero characteristics of Alonso's rear wing with flow-vis paint, but its programme was set back when Kimi Raikkonen had a water pump failure that took half an hour to resolve.
Raikkonen returned to the track but, in spite of completing a respectable number of laps, set a best time of 1m20.210 that was only eighth fastest overall.
McLaren sported a fresh look, with a new rear wing design featuring sophisticated detailing around the endplates, and a new race engineer for Jenson Button: Olympic rowing medallist Tom Stallard.
They had a reasonably encouraging session, Button completing 24 laps and Kevin Magnussen 32, finishing fifth and seventh quickest.
Williams tester Susie Wolff enjoyed a lengthier stint in the cockpit than she did at Silverstone, despite a scare in the opening minutes when her FW36 slowed with a sensor issue.
She closed out the session just two tenths of a second off the pace of Felipe Massa, well under the half-second benchmark the team had set.
There was a substantial gap between the runners at the bottom end of the timesheets as Lotus, Caterham and Marussia languished over two seconds off the pace.
Romain Grosjean had a rear wing failure that caused his DRS to stick open under braking in a high-speed section, while Max Chilton brought up the rear after a number of power unit problems.
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- Motor Racing
- Lewis Hamilton
- Fernando Alonso
- Jenson Button
- Sebastian Vettel