Marc Marquez headed Valentino Rossi by 0.396 seconds in the opening MotoGP practice session for the Americas Grand Prix weekend.
Marquez – who has won every race in Texas and qualified on pole for all of them – got down to business straight away in FP1, the Honda rider going two seconds clear of the rest with his early effort of 2:07.049s.
Ducati's Jorge Lorenzo cut Marquez's advantage down to a second 15 minutes in, with Maverick Vinales edging a fraction closer with a 2:07.815s five minutes later.
Marquez upped his pace again midway through with a 2:06.815s, improving on his follow-up tours to a 2:06.126s and a 2:06.092s, though his gap to the rest was down to just over half a second thanks to Vinales.
The Honda rider continued to chip away at his best laps, a succession of session bests culminating in a 2:05.530s on a significantly used Medium rear tyre.
In contrast, Rossi used his fresh Soft front and rear slicks to jump up to second in the closing stages with a 2:05.926s, with Yamaha team-mate Vinales three-tenths further back in third – the Spaniard mirroring Marquez's tyre choice.
After a difficult Argentina weekend, in which he came away with just one point, Lorenzo ended FP1 in a more positive fashion, the Ducati rider two-tenths behind Vinales and ahead of Termas race winner and championship leader Cal Crutchlow.
Lorenzo's Ducati stablemate Andrea Dovizioso put the second of the GP18s sixth, with rookie Takaaki Nakagami an impressive seventh on his year-old RC213V.
Andrea Iannone was lead Suzuki runner in eighth, with Alex Rins two-tenths down at the foot of the top 10. Johann Zarco was sandwiched between the pair in ninth, the Frenchman's session getting off to a troubled start when Tech3 YZR-M1 expired in the opening minutes.
Dani Pedrosa is present at the Circuit of the Americas just 10 days after surgery on a fracture right wrist, though he struggled to 21st on the timesheets ahead of Karel Abraham, while Argentina poleman Jack Miller was a low-key 23rd.
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