Lewis Hamilton pipped Formula 1 title rival Nico Rosberg to the fastest time on the opening day of practice for the German Grand Prix.
Rosberg had been the faster of the Mercedes pair early in the session while on the slower soft-compound Pirellis, outpacing Hamilton by just over three tenths of a second.
But the world championship leader made a mistake at Turn 2 on his first flying lap on super-soft rubber, meaning he was unable to improve his time until his next lap.
Hamilton then put in a 1m18.341s on his first flier, setting the fastest time in the middle sector, with Rosberg ending up 24 thousandths of a second slower.
Mercedes later had a problem in the pits when Hamilton came in unexpectedly and the team had Rosberg's tyres ready, meaning that it took time to get his correct tyres.
With Hamilton sat in the pits, Rosberg came in and had to queue to wait for the team to put on the correct tyres amid concerns about his brakes overheating.
Daniel Ricciardo was third fastest for Red Bull, just a tenth off the pace, with Ferrari driver Kimi Raikkonen a strong fourth, half a second down.
Kevin Magnussen continued his recent run of impressive form with fifth fastest, just ahead of Williams driver Felipe Massa, who was briefly second fastest in the early stages of the super-soft runs.
World champions Jenson Button and Fernando Alonso were eighth and ninth fastest, the former failing to extract as big an improvement on super-soft rubber as those at the front.
Sauber driver Adrian Sutil was 11th fastest for Sauber ahead of Daniil Kvyat, with Force India pairing failing to break the top 10 for the second grand prix Friday in a row in 13th and 14th place.
Caterham had a troubled session, with both cars stopping on the circuit.
Kamui Kobayashi parked with flames emerging from the rear of the car after completing 12 laps, while Marcus Ericsson was ordered to stop his car on track because of a drop in oil pressure after just three laps.
But the team did get Ericsson's car back and he was able to return to the track in the final half hour, allowing him to set the 20th fastest time.
With the ambient temperature at over 30C throughout the afternoon, track temperatures hit 58C, the highest so far this season.
Pos Driver Team Time Gap Laps
1. Lewis Hamilton Mercedes 1m18.341s 38
2. Nico Rosberg Mercedes 1m18.365s +0.024s 39
3. Daniel Ricciardo Red Bull-Renault 1m18.443s +0.102s 35
4. Kimi Raikkonen Ferrari 1m18.887s +0.546s 38
5. Kevin Magnussen McLaren-Mercedes 1m18.960s +0.619s 40
6. Felipe Massa Williams-Mercedes 1m19.024s +0.683s 36
7. Jenson Button McLaren-Mercedes 1m19.221s +0.880s 40
8. Sebastian Vettel Red Bull-Renault 1m19.248s +0.907s 35
9. Fernando Alonso Ferrari 1m19.329s +0.988s 32
10. Valtteri Bottas Williams-Mercedes 1m19.385s +1.044s 34
11. Adrian Sutil Sauber-Ferrari 1m19.417s +1.076s 41
12. Daniil Kvyat Toro Rosso-Renault 1m19.452s +1.111s 27
13. Sergio Perez Force India-Mercedes 1m19.581s +1.240s 28
14. Nico Hulkenberg Force India-Mercedes 1m19.593s +1.252s 32
15. Jean-Eric Vergne Toro Rosso-Renault 1m19.760s +1.419s 32
16. Pastor Maldonado Lotus-Renault 1m20.158s +1.817s 35
17. Romain Grosjean Lotus-Renault 1m20.358s +2.017s 35
18. Esteban Gutierrez Sauber-Ferrari 1m20.504s +2.163s 40
19. Jules Bianchi Marussia-Ferrari 1m21.328s +2.987s 31
20. Marcus Ericsson Caterham-Renault 1m21.870s +3.529s 21
21. Max Chilton Marussia-Ferrari 1m21.898s +3.557s 28
22. Kamui Kobayashi Caterham-Renault 1m23.728s +5.387s 12