Nico Rosberg bounced back from a hydraulic leak to pip Lewis Hamilton in first practice for the British Grand Prix.
With the sun beating down on the Silverstone circuit, Rosberg and Hamilton immediately jumped to the top of the timesheets with the German holding the early advantage.
However, a hydraulic problem forced him to pull over onto the side of the track after just five laps.
While Rosberg was sidelined, Hamilton had it all his own way to finish the morning with a 1:34.344.
Although that time looked as if it would go unchallenged, Rosberg's late return saw him grab the P1 slot by 0.010s just moments before the chequered flag fell.
Coming to complete his final flying lap, he lowered the benchmark to a 1:34.274. That gave him a 0.070s advantage over Hamilton.
Max Verstappen was third fastest in what was a relatively quiet session with large periods of inactivity, 1.2s off the pace, while a late burst from Kimi Raikkonen moved him up to fourth place overall.
Carlos Sainz finished fifth ahead of Sebastian Vettel, Daniel Ricciardo, who complained of brake issues throughout the session, and Daniil Kvyat.
Nico Hulkenberg, putting in the laps in the B-spec Force India, was ninth quickest, 1.883s down. Felipe Massa completed the top ten.
It was another difficult start to a weekend for McLaren as both Fernando Alonso and Jenson Button and Fernando Alonso spent large periods in the pits. They were P17 and P18 respectively.
1 Nico Rosberg Mercedes 1:34.274 12 laps
2 Lewis Hamilton Mercedes 1:34.344 0.070 26 laps
3 Max Verstappen Toro Rosso 1:35.530 1.256 18 laps
4 Kimi Raikkonen Ferrari 1:35.588 1.314 21 laps
5 Carlos Sainz Toro Rosso 1:35.669 1.395 33 laps
6 Sebastian Vettel Ferrari 1:35.739 1.465 17 laps
7 Daniel Ricciardo Red Bull 1:35.818 1.544 26 laps
8 Daniil Kvyat Red Bull 1:35.876 1.602 22 laps
9 Nico Hulkenberg Force India 1:36.157 1.883 28 laps
10 Felipe Massa Williams 1:36.469 2.195 23 laps
11 Felipe Nasr Sauber 1:36.855 2.581 20 laps
12 Sergio Perez Force India 1:36.889 2.615 26 laps
13 Susie Wolff Williams 1:37.242 2.968 19 laps
14 Jolyon Palmer Lotus 1:37.262 2.988 26 laps
15 Raffaele Marciello Sauber 1:37.372 3.098 17 laps
16 Pastor Maldonado Lotus 1:38.080 3.806 8 laps
17 Fernando Alonso McLaren 1:38.222 3.948 12 laps
18 Jenson Button McLaren 1:38.860 4.586 10 laps
19 Will Stevens Manor 1:38.981 4.707 23 laps
20 Roberto Merhi Manor 1:40.477 6.203 23 laps