Spa-Francorchamps, Belgium - Lewis Hamilton lapped six tenths of a second faster than Mercedes team-mate Nico Rosberg in a twice halted Belgian Grand Prix practice session on Friday.
After championship leader Rosberg had set the pace in the morning with a lap just 0.097sec faster than Hamilton's best, the Briton turned the tables after lunch with a substantially quicker effort.
His time of 1m49.189 was 0.604sec better than Rosberg's on a cloudy but bright day at the longest track on the calendar, where the weather can combine the seasons in the space of an afternoon.
Rosberg had topped the first session timesheets in 1m51.577s as the two title rivals - separated by just 11 points after 11 of 19 races - renewed their duel after the August break with their domination intact.
The afternoon running was interrupted when Pastor Maldonado crashed his Lotus into the barriers on the way to Pouhon.
There was a further stoppage in the first half hour when Mexican Esteban Gutierrez's Sauber spun and was stranded on the track at Blanchimont.
Ferrari's Fernando Alonso was third fastest in both sessions with McLaren's Jenson Button fourth in the morning and fifth in the afternoon.
The Mercedes-powered teams were predicted to dominate and had seven cars in the top 10 in the opening session.
But Ferrari's showing, with four times Spa winner Kimi Raikkonen fifth fastest in the morning despite a spin at La Source, indicated they would not have it all their own way.
Williams had a low-key start, with Valtteri Bottas 10th on the timesheets and Felipe Massa 15th, but picked up with Massa fourth in the afternoon.
Red Bull's Daniel Ricciardo, winner of the previous race in Hungary, was ninth and eighth in the two sessions while his quadruple world champion team mate Sebastian Vettel sat out the second session due to an electrical problem that forced an engine change.
At the bottom end of the field, Andre Lotterer limbered up for his F1 debut with Caterham as a replacement for Kamui Kobayashi by lapping faster than Swedish rookie team mate Marcus Ericsson in the morning.
American Alexander Rossi replaced Max Chilton for the morning session at Marussia but his hopes of completing the weekend and racing for the first time evaporated when the Briton was reinstated following contractual wrangles. - Reuters
RESULTS - SECOND SESSION
1. Lewis Hamilton (Britain) Mercedes - 1m49.189s
2 Nico Rosberg (Germany) Mercedes - 1:49.793
3 Fernando Alonso (Spain) Ferrari - 1:49.930
4 Felipe Massa (Brazil) Williams - 1:50.327
5 Jenson Button (Britain) McLaren - 1:50.659
6 Valtteri Bottas (Finland) Williams - 1:50.677
7 Daniil Kvyat (Russia) Toro Rosso - 1:50.725
8 Daniel Ricciardo (Australia) Red Bull - 1:50.977
9 Kevin Magnussen (Denmark) McLaren - 1:51.074
10 Nico Huelkenberg (Germany) Force India - 1:51.077
11 Jean-Eric Vergne (France) Toro Rosso - 1:51.383
12 Adrian Sutil (Germany) Sauber - 1:51.450
13 Sergio Perez (Mexico) Force India - 1:51.573
14 Romain Grosjean (France) Lotus - 1:52.196
15 Kimi Raikkonen (Finland) Ferrari - 1:52.234
16 Jules Bianchi (France) Marussia - 1:52.776
17 Esteban Gutierrez (Mexico) Sauber - 1:53.955
18 Max Chilton (Britain) Marussia - 1:54.040
19 Marcus Ericsson (Sweden) Caterham - 1:54.050
20 Andre Lotterer (Germany) Caterham - 1:54.093
21 Pastor Maldonado (Venezuela) Lotus
22 Sebastian Vettel (Germany) Red Bull
1 Nico Rosberg (Germany) Mercedes – 1m51.577s
2 Lewis Hamilton (Britain) Mercedes - 1:51.674
3 Fernando Alonso (Spain) Ferrari - 1:51.805
4 Jenson Button (Britain) McLaren - 1:52.404
5 Kimi Raikkonen (Finland) Ferrari - 1:52.818
6 Sergio Perez (Mexico) - Force India - 1:52.903
7 Kevin Magnussen (Denmark) McLaren - 1:52.922
8 Nico Huelkenberg (Germany) - Force India - 1:52.937
9 Daniel Ricciardo (Australia) Red Bull - 1:52.972
10 Valtteri Bottas (Finland) Williams - 1:53.172
11 Sebastian Vettel (Germany) Red Bull - 1:53.369
12 Daniil Kvyat (Russia) Toro Rosso - 1:53.594
13 Romain Grosjean (France) Lotus - 1:53.597
14 Adrian Sutil (Germany) Sauber - 1:53.703
15 Felipe Massa (Brazil) Williams - 1:53.968
16 Jean-Eric Vergne (France) Toro Rosso - 1:54.189
17 Giedo van der Garde (Netherlands) Sauber - 1:54.335
18 Pastor Maldonado (Venezuela) Lotus - 1:55.336
19 Jules Bianchi (France) Marussia - 1:55.782
20 Alexander Rossi (United States) Marussia - 1:57.232
21 Andre Lotterer (Germany) Caterham - 1:57.886
22 Marcus Ericsson (Sweden) Caterham - 1:57.977