Mercedes driver Lewis Hamilton topped the timesheet in the first practice session of the United States Grand Prix in Austin, Texas.
The reigning world champion is in danger of losing his title to teammate Nico Rosberg as the Brit currently sits 33 points adrift of his rival with 100 points on offer in the remaining four races.
Hamilton edged ahead in the first practice of the day on Friday, while Rosberg clocked the second-quickest time and Red Bull's Max Verstappen the third.
Kimi Raikkonen recorded the fourth-fastest lap of the session, but his Ferrari teammate Sebastian Vettel encountered some trouble when a piece of bodywork was ripped off the front of his vehicle after he ran off the track at Turn 18.
Elsewhere, 22-year-old Briton Jordan King drove his first F1 car today as he tested Pascal Wehrlein's Manor to clock the 19th-fastest time.
First practice standings:
1. Lewis Hamilton (Mercedes)
2. Nico Rosberg (Mercedes)
3. Max Verstappen (Red Bull)
4. Kimi Raikkonen (Ferrari)
5. Nico Hulkenberg (Force India)
6. Valtteri Bottas (Williams)
7. Daniel Ricciardo (Red Bull)
8. Sebastian Vettel (Ferrari)
9. Daniil Kvyat (Toro Rosso)
10. Carlos Sainz Jr (Toro Rosso)
11. Felipe Massa (Williams)
12. Felipe Nasr (Sauber)
13. Fernando Alonso (McLaren)
14. Romain Grosjean (Haas)
15. Esteban Gutierrez (Haas)
16. Alfonso Celis (Force India)
17. Jenson Button (McLaren)
18. Kevin Magnussen (Renault)
19. Jordan King (Manor)
20. Marcus Ericsson (Sauber)
21. Jolyon Palmer (Renault)
22. Esteban Ocon (Manor)
