Reigning MotoGP champion Marc Marquez set the pace in second practice at Austin, leading the way by just under three tenths of a second.
It was Marquez who controlled the session early on, the Honda rider firing in a lap of 2m05.004s to lead Yamaha's Maverick Vinales by seven tenths.
Unbeaten at the circuit in four starts, Marquez followed that up with a 2m04.622s, beating Vinales' FP1-topping effort of 2m04.923s.
Vinales became the afternoon's second rider to dip beneath the 2m05s barrier halfway through the session on his second run, setting a 2m04.945s.
He subsequently closed on Marquez further with a 2m04.837s lap, before grabbing the top spot with a 2m04.451s with 18 minutes to go.
That stood as the benchmark until the dying stages of the 45-minute session, when Tech3 Yamaha rider Johann Zarco used soft tyres to eclipse Vinales with a 2m04.347s.
Marquez, running a medium front and soft rear, was soon back on top, though, recording a 2m04.061s on his final run that was enough to beat Zarco by 0.286 seconds.
Vinales did not use a soft tyre at the end of the session or improve, but his earlier time on medium tyres was enough for third, 0.390s slower than Marquez.
Valentino Rossi made it two Yamahas in the top four on his final run, albeit winding up 0.355s slower than team-mate Vinales and 0.745s off the pace of Marquez.
Fifth was the second factory Honda of Dani Pedrosa, followed by Andrea Dovizioso on the best of the Ducatis and Cal Crutchlow's LCR Honda, while Zarco's team-mate Jonas Folger was last of those to get within a second of Marquez.
Pramac Ducati's Scott Redding and Suzuki's Andrea Iannone completed the top 10, with Jorge Lorenzo on the second Ducati just behind in 11th with a best time 1.221s off the pace.
Iannone's team-mate Alex Rins suffered an apparent engine failure on his first lap out of the pits, although the Spaniard was able to switch to his second bike and finish the session 18th.
KTM rider Pol Espargaro tried a new winglet-substitute front fairing on his way to the 20th-fastest time of the session, 2.442s behind Marquez.
Avintia Ducati's Loris Baz at Turn 1 and Aspar Ducati's Karel Abraham exiting Turn 11 both crashed late in the session, Abraham cleared of injury following a trip to the medical centre.
PRACTICE TWO TIMES: