Francesco Bagnaia bested Alex Marquez to claim victory in Texas and take the lead in the Moto2 points standings.
Marquez converted pole position into the holeshot ahead of Mattia Pasini, Bagnaia and Sam Lowes, while Marquez's Marc VDS team-mate Joan Mir plummeted to 24th after he was punted wide by Luca Marini.
Already a second clear of Pasini by the end of the first lap, Marquez ran comfortably in the lead for the next seven laps, while Bagnaia moved ahead of Pasini, who struggled for pace in the early stages as the sole runner on the hard rear tyre.
By lap eight Bagnaia had cut Marquez's advantage down to just under half a second, with the latter lucky to remain in the lead after a massive moment exiting Turn 18 several tours later.
Bagnaia took the lead away from Marquez at the first corner on lap 13, though the Marc VDS rider retaliated with a daring move at Turn 3.
The pair traded positions again at Turn 11, with Bagnaia gaining the upper hand into Turn 12. The Italian proceeded to open up a gap of half a second, but Marquez dug deep to try to reclaim the lead at Turn 12 on the next lap.
The Spaniard was unable to stick the move, however, and Bagnaia was able to ease a second clear, while Red Bull KTM Ajo's Miguel Oliveira closed in on Marquez over the final laps.
Bagnaia eased to the chequered flag, while Marquez was able to stall Oliveira's charge to second, with Mir recovering to fourth after his earlier off.
Iker Lecuona mugged Brad Binder on the run to the line to secure his best-ever result in the class, while Mattia Pasini surrendered his championship lead to Bagnaia by 10 points after finishing a distant seventh.
Jorge Navarro brushed off his 19th-place grid slot to sntach eighth in the end, with Dominique Aegerter – who was caught up in the incident at the start along with Mir – and Lorenzo Baldassarri completing the top 10.
Both Dynavolt riders were set for top six results, but both crashed out, with Marcel Schrotter suffering a nasty highside exiting Turn 1 on lap seven while running fourth, and Xavi Vierge sliding out of sixth in the closing stages.
Stefano Manzi and Danny Kent also crashed out, while Sam Lowes – who started second – remounted after a fall at Turn 18 on the first lap to finish 24th.