The lights-to-flag win on Sunday completed a perfect weekend in Austin for resurgent Red Bull driver Verstappen after the four-time world champion also won Saturday's sprint from pole.
Lando Norris sealed second after winning a race-long tussle with Ferrari's Charles Leclerc in the closing stages as the British driver reduced McLaren team-mate Piastri's championship lead to 14 points after the Australian finished only fifth.
Verstappen's 33 points from the weekend mean he has reduced his own deficit to Piastri to 40 points - from 63 - following the costly collision during the sprint which dumped both McLarens out.
The Red Bull driver declared his bid for a fifth straight title over before the summer break, but he has slashed the gap to Piastri from 104 points after Zandvoort five races ago.
That race was the last win for the previously-dominant McLaren pair as a genuine three-way title scrap has emerged, with five rounds remaining and 141 points left to fight for.
Piastri will have the most to ponder ahead of Mexico next weekend, having been beaten by both Norris and Verstappen in each of the last four races.
Leclerc claimed third with Lewis Hamilton fourth on an improved day for Ferrari as George Russell finished sixth for Mercedes.
Norris' chances of threatening Verstappen at the Circuit of the Americas were dashed as he was undone by the fast-starting Leclerc, the only one of the top 15 to begin on soft tyres.
The Ferrari driver used his extra grip to charge round the outside of turn one and past Norris on the inside at turn two as Piastri gained a place from sixth and Hamilton jumped to fourth, with Russell slipping two places from fourth.
Russell attempted to hit back at Piastri but was thwarted as Norris' battle to get past Leclerc allowed Verstappen to pull clear out front.
Norris attacked Leclerc at turn 12 on lap three and four but could find no way through. It was a dream scenario for Verstappen, who had a three-second lead by lap five.
Norris bided his time before launching another sustained attack on Leclerc on lap 15, but the Monegasque's resolute defence continued to ruin the British driver's hopes of victory, now over seven seconds behind Verstappen.
Norris finally got the move done on Leclerc on lap 21 but had another concern as he was shown a black-and-white flag for track limits, meaning one more would result in a penalty.
Piastri pitted after lap 30, with Norris in two laps later only to emerge once again behind Leclerc after a sluggish stop.
Norris complained that his used set of soft tyres had "gone" with 16 laps still to go and he dropped away behind Leclerc.
His race engineer told him to cool the tyres before attacking again and he did just that, hunting down Leclerc and getting through at turn 12 with five laps remaining.
Piastri was off the pace all weekend and that did not change in the closing stages as the title leader trudged home in fifth.
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