Hamilton and Rosberg traded fast times, with interventions from Ferrari's Kimi Raikkonen and Red Bull's Sebastian Vettel, before Alonso moved ahead in a F14 T likely to have been running minimal fuel. The Spaniard's best lap was 1m 49.056s compared to Hamilton's 1m 49.178s and Rosberg's 1m 49.205s.
Behind them, Vettel clung on in fourth place on 1m 49.874s ahead of team mate Daniel Ricciardo on 1m 50.122s, but the session ended badly for Red Bull when Vettel pulled into the pit entry road with a suspected engine issue and then helped his crew to push the stricken RB10 back to his pit.
Jean-Eric Vergne overcame early brake problems to go sixth fastest for Toro Rosso on 1m 50.539s, but later stopped with a suspected ERS problem.
Raikkonen fell back to seventh on 1m 50.783s, as Jenson Button overcame some early delays and ride height problems which did not see him run until the 37th minute to take eighth for McLaren on 1m 50.922s ahead of traffic-frustrated Daniil Kvyat on 1m 50.990s in the second STR9.
The Force India's of Sergio Perez and Nico Hulkenberg sandwiched Kevin Magnussen's McLaren in 10th to 12th places, on 1m 51.131s, 1m 51.217s and 1m 51.604s respectively.
Williams ran, as has often been the case this season on a Friday, relatively low down in the order with Felipe Massa their faster runner with 1m 51.953s for 13th place. Pastor Maldonado's Lotus separated the Brazilian from team mate Valtteri Bottas, the Venezuelan lapping in 1m 52.125s for 14th and the Finn in 1m 52.146s for 15th.
Esteban Gutierrez recovered well from a control unit issue which kept him in the Sauber garage for the first 70 minutes, to pip team mate Adrian Sutil 1m 52.171s to 1m 52.237s.
Romain Grosjean in the second Lotus had some off-road adventures, as did Maldonado, on his way to 1m 52.906s and 18th place.
At the back Jules Bianchi fought understeer and ERS charging problems to vault ahead of the Caterhams, after lapping his Marussia in 1m 54.113s; the green cars were next with Marcus Ericsson on 1m 54.475s and Kamui Kobayashi on 1m 54.607s, as Max Chilton brought up the rear on 1m 55.170s in the second Marussia.
There were several explorations of track limits, with Vettel brushing the wall in Turn 21 with his right front wheel, Kobayashi spinning at Turn 5, and Perez, Sutil, and Rosberg all running wide.