Andrea Iannone snatched top spot away from early crasher Marc Marquez by 0.056 seconds in MotoGP FP2 in Texas, while Johann Zarco missed the provisional Q2 cut in 13th.
FP1 pacesetter Marquez took over from Iannone at the top of the timesheets in the opening minutes of the afternoon session, the Honda rider easing eight tenth clear with a 2:06.076s.
On his second flying lap, Marquez was already under his best pace from the morning with a 2:05.287s, which he duly improved to a 2:04.963s at just under mid distance before crashing at Turn 11 just moments later.
Getting away relatively lightly from the front end fold, he was not of action for too long, nor did his fastest lap come under threat.
Ducati's Jorge Lorenzo cut the Honda man's advantage down from eight tenths to just under six with just over five minutes to go, while Marquez found a fraction more with a 2:04.951s.
Marquez improved further to a 2:04.655s, set on a used hard rear tyre, and looked set to remain on top. However, a final lap of 2:04.599s from Iannone put the Italian half a tenth clear of the Honda rider – albeit, that time set using a fresh soft rear slick.
Maverick Vinales ended the day third fastest, two tenths shy of Iannone, with Yamaha teammate Valentino Rossi a further tenth adrift in fourth.
Championship leader Cal Crutchlow secured fifth in the latter stages of the session on his LCR Honda, the Briton four tenths clear of the second factory GSX-RR of Alex Rins.
Lorenzo headed Ducati teammate Andrea Dovizioso in seventh, the latter lifting himself into eighth at the death having languished down in 16th for much of the 45-minute session.
Aleix Espargaro leaped up to ninth on his Aprilia, edging ahead of the injured Dani Pedrosa, who has potentially secured the final place in the second qualifying session with rain threatening Saturday's running.
Should the weather take a turn for the worse for third practice, Tech3's Zarco will find himself facing Q1 along with Argentina poleman Jack Miller after another tricky session for the Frenchman in 13th.
Along with Marquez, Honda stablemate Takaaki Nakagami [17th] on the second LCR bike suffered a fall at the end of the FP2, while Pol Espargaro [23th] threw his KTM at the scenery of Turn 15 midway through the session while testing a new aerodynamic fairing on his RC16.
