Austin MotoGP: Marc Marquez flies in opening practice

The world champion's Honda was over a second clear of the field until improvements from Aleix Espargaro and Dani Pedrosa reduced Marquez's advantage to a relatively small 0.887 seconds.

Marquez's opening runs had left him 1.6s faster than anyone else early on. He eventually got down to a 2m04.704s at the track where he took his maiden MotoGP win in only his second start 12 months ago.

Until his final run, Open class rider Espargaro had been outside the top 10 and looking unlikely to repeat his giantkilling practice form from Qatar last month.

But his late jump up the order allowed the Forward Racing man to split the factory Hondas in the top three.

Espargaro and Pedrosa's progress relegated Valentino Rossi to fourth on the top Yamaha.

Rossi's team-mate Jorge Lorenzo was back in 12th and again appeared to be expressing his unhappiness with the bike's handling in the pits between runs.

Andrea Dovizioso completed the top five on the fastest Ducati.

His team-mate Cal Crutchlow claimed seventh in the end behind Bradley Smith, despite having to abandon an early run and 'scoot' his bike back down the pitlane after a technical problem emerging as he tried to set off.

Gresini's Alvaro Bautista and Aspar's Nicky Hayden also had technical issues during the morning, Bautista's coming right at the start of his out-lap.

Pos Rider              Bike                    Time       Gap     Laps
 1. Marc Marquez       Honda                   2m04.704s           15  
 2. Aleix Espargaro    Forward Yamaha          2m05.591s  +0.887s  13  
 3. Dani Pedrosa       Honda                   2m05.676s  +0.972s  15  
 4. Valentino Rossi    Yamaha                  2m05.972s  +1.268s  15  
 5. Andrea Dovizioso   Ducati                  2m06.279s  +1.575s  14  
 6. Bradley Smith      Tech 3 Yamaha           2m06.336s  +1.632s  18  
 7. Cal Crutchlow      Ducati                  2m06.433s  +1.729s  15  
 8. Stefan Bradl       LCR Honda               2m06.537s  +1.833s  15  
 9. Andrea Iannone     Pramac Ducati           2m06.602s  +1.898s  14  
10. Alvaro Bautista    Gresini Honda           2m06.633s  +1.929s  13  
11. Pol Espargaro      Tech 3 Yamaha           2m06.680s  +1.976s  17  
12. Jorge Lorenzo      Yamaha                  2m06.771s  +2.067s  14  
13. Nicky Hayden       Aspar Honda             2m07.450s  +2.746s  13  
14. Colin Edwards      Forward Yamaha          2m07.644s  +2.940s  15  
15. Yonny Hernandez    Pramac Ducati           2m07.689s  +2.985s  16  
16. Karel Abraham      Cardion Honda           2m07.702s  +2.998s  13  
17. Hector Barbera     Avintia FTR-Kawasaki    2m08.150s  +3.446s  16  
18. Hiroshi Aoyama     Aspar Honda             2m08.455s  +3.751s  17  
19. Scott Redding      Gresini Honda           2m08.588s  +3.884s  14  
20. Danilo Petrucci    Ioda Aprilia            2m09.646s  +4.942s  13  
21. Broc Parkes        PBM Aprilia             2m10.206s  +5.502s  15  
22. Michael Laverty    PBM Aprilia             2m10.493s  +5.789s  12  
23. Mike di Meglio     Avintia FTR-Kawasaki    2m11.100s  +6.396s  15