Vettel leading Hamilton early in the race.
Alonso now sits 13 points behind the German with just one race remaining after the pair both finished on the podium in Austin. Vettel will now be guaranteed the title should he finish higher than fourth in Brazil next week.
The day got off to a fantastic start for Alonso, who was promoted two places on the grid before the race. After Romain Grosjean was penalised five grid places for a gearbox change, Ferrari deliberately broke the seal on Felipe Massa’s, so he suffered the same penalty.
That meant Alonso was not just two places further up the grid; more importantly, he was on the clean side of the track. The move worked, as Alonso found himself in fourth place after a clean first corner.
Vettel stayed cool under pressure and retained his place at the front of the pack as teammate Mark Webber jumped ahead of Hamilton into second, the German quickly pulling away into a two-second lead after the first lap.
Worries about a lack of overtaking on the brand-new Circuit of the Americas were quashed very early in the race, as Hamilton regained second place from Webber whilst drivers in the middle of the field swapped places routinely.
Alonso, knowing he needed to finish at least fourth to keep his title hopes alive, found himself promoted to third place when the Red Bull of Webber suffered his first mechanical failure in three years after just 18 laps.
Normally incredibly efficient in the pit lane, a rare error from the Ferrari pit crew left Alonso in danger of losing a place to Kimi Raikkonen, but a similarly poor pit stop from the Lotus crew let Alonso, and Ferrari off the hook.
Will Vettel win the World Title in Brazil?
Hamilton pushed Vettel hard once the pair had switched to the harder tyres, until Hamilton eventually took advantage of DRS and passed the German to take the race lead with 14 laps remaining.
The Red Bull driver was not very happy about the pass, claiming he was impeded by a back marker, allowing Hamilton to close the gap and get into the DRS zone.
Massa had a strong race to finish fourth despite taking that penalty to assist his teammate Alonso, but it was Jenson Button who showed his racing skills off to the American crowd, moving up from 16th after a poor start to finish in fifth.
But despite a fantastic drive from both McLaren drivers, all eyes were fixed on the title battle. Alonso seemed resigned to his slower pace and sat in clear air for almost the entire race hoping for a mistake from Vettel.
Whilst Hamilton did manage to pass Vettel to take the win, Alonso never looked like finishing ahead of his championship rival as he did in Abu Dhabi two weeks ago. Instead, their positions on the podium were reversed, and Vettel will take a 13-point lead into the final race in Brazil.