Rosberg secured top spot courtesy of a 1m 25.887s on Pirelli's medium compound, with Hamilton - who had been slower on the hards - choosing to abandon his own attempt. He therefore had to be content with 1m 26.756s on the hards, which was enough for him to take second place.
While Mercedes' advantage could not be disguised, it was at least very close behind the two Silver Arrows. Fernando Alonso was third fastest after a medium-tyre run for Ferrari, but his 1m 27.188s was 1.3s slower than Rosberg. Felipe Massa was just three hundredths of a second down the road for Williams, having jumped into fourth with a late 1m 27.223s, while Romain Grosjean finally got his Lotus E22 going well, despite some instability under braking, to take an encouraging fifth place on 1m 27.682s.
Kevin Magnussen was sixth for McLaren on 1m 27.806s, a time which Daniel Ricciardo narrowly failed to match. The Australian's Red Bull clocked 1m 27.808s. Jenson Button was right behind them with 1m 28.006s in the second MP4-29, with Pastor Maldonado making it two Lotuses in the top 10 with 1m 28.0756s. Red Bull's Sebastian Vettel rounded out the top 10 with 1m 28.085s, less than one tenth of a second slower than Button.
A late run brought Valtteri Bottas up to 11th in the second Williams on 1m 28.101s, as Jean-Eric Vergne pipped Toro Rosso team mate Daniil Kvyat, with 1m 28.242s to 1m 28.298s.
Kimi Raikkonen didn't better 1m 28.419s in the second Ferrari, leaving him down in 14th ahead of the Force Indias and the Saubers. Sergio Perez was the faster of the former with 1m 28.571s to Nico Hulkenberg's 1m 28.668s, as Adrian Sutil led Esteban Gutierrez for the latter with 1m 28.715s to 1m 28.865s.
Max Chilton's session was brought to an early halt when he slid off into the gravel at Turn 5, but he still managed to outpace Marussia team mate Jules Bianchi, with 1m 30.169s to 1m 30.670s. The Frenchman suffered a puncture on what was his only run on the medium tyres.
Kamui Kobayashi's late attempt to better 1m 30.712s failed when his Caterham ran into (and out of) a gravel trap, while team mate Marcus Ericsson was 22nd on 1m 31.559s.