Surprisingly, this was Hamilton's first win since Germany in July. It couldn't have been better timed.
The Briton needed this result in order to keep his slim title hopes alive. Seven points have been taken out of Rosberg's lead - now down to 26 points - but more importantly, a warning shot has been fired. Hamilton isn't about to give this one up. Rosberg still only needs to finish second twice and third once to clinch the title, but he has never been here before - which, along with victory, will give Hamilton some hope that he can yet turn things around.
There was another reason victory was significant. This was Hamilton's fifth in the United States, his fourth (from five races) in Austin - and it also made him only the third man in history to win 50 Grands Prix (after Michael Schumacher and Alain Prost).
"I had completely forgotten that it was going to be the 50th,” he chuckled afterward. "It's been a long time coming. Once again, and I know I've mentioned it before but I've been here for 10 years, I've had lots of ups and downs and lots of great opportunities to work with some incredibly gifted people who have helped me get here today.
"Then my family as well, without whom I wouldn't be here today. It's kind of very surreal, for sure. I can't believe that there are only three of us, but hopefully on to bigger and better things."
Nico Rosberg and his title aspirations
The points leader didn't score a 10th victory of the season, and he got beaten by his team mate, but he did exactly what he needed to in terms of the championship fight. A smooth, fast and intelligent race earned him second - and when it might have been tempting to stroke it home, he kept the hammer down and pushed as hard as he could to the flag.
Haas on home soil
After eight races without scoring points, Haas couldn't have timed their return to form better. Esteban Gutierrez was in contention for points right up until brake problems once again bit, but Romain Grosjean's 10th-place finish was a confirmation of the calibre of Gene Haas's eponymous team.
Alonso - and McLaren
After the low of Suzuka, it was important for McLaren to fight back in Austin - a message Alonso apparently took to heart. A superb performance, and some typically opportunistic and brilliant overtakes, lifted him to fifth at the flag. With only Mercedes, Red Bull and Ferrari ahead, the Spaniard maximised everything at his disposal on Sunday - another reminder, as if it were needed, of his class.
The good news for the team was backed up by Jenson Button climbing from 19th to finish ninth - only the fourth time this season that both cars have scored points.
He may not have been able to prevent Alonso snatching fifth late on, but the pair's battle lit up the final laps in Austin - and reaffirmed Sainz's reputation as one of the best young drivers on the grid. Sixth still equalled his best ever F1 result, and moved him well clear of Grosjean in the fight for 12th in the championship. And to cap it all off, he and Alonso then celebrated together with dinner on Sunday night - a lovely show of admiration and respect from the Spanish compatriots.
The saga of Mercedes’ clutches has been ongoing and painful, since 2015, and had cost both drivers better results at times this season. But after prolonged sessions with the engineers back at Brackley during the recent celebrations of the team’s third successive world championship for constructors, both Hamilton and Rosberg went to Texas confident that things would be better. They were. Neither had a problem and both made strong starts. Job done.
The Circuit of The Americas
One year ago we had the sight of atrocious weather severely affecting a race everyone in F1 has come to love. This year was a very different picture.
Thanks to some great promotion and determination and a striking concert from Taylor Swift, Austin was back in style. Swift helped to pull in even more fans and the 266,889 spectators who flocked in over the three days made it a record attendance.
A race to forget - quickly - for the Prancing Horse.
After the strong showing in Suzuka, it was a big disappointment to Ferrari that their upward progress did not continue in Austin. Clearly they did not have the pace to run with either Mercedes or Red Bull - and while Vettel did lead for three laps, it was only by virtue of stretching out his opening stint on the supersoft tyres.
He at least finished, but was a distant fourth, 43s from the lead Mercedes. The four-time world champion has scored just one podium in his last 10 races - his worst run of form since his maiden full season with Toro Rosso in 2008.
Raikkonen didn't even make it to the chequered flag: his strong showing ended ignominiously with a loose right wheel after his second stop on the 38th lap. Rubbing salt into the wound, the stewards fined the team 5000 euros for an unsafe release.
The Dutchman didn't make a great start, losing a place to Kimi Raikkonen's supersoft-shod Ferrari, but on his soft tyres he was trading lap times with Hamilton and looked strong when fighting for third with Nico Rosberg. His race began to unravel on lap 26, though, when he pitted unannounced - a mistake he took the blame for after the race. That dropped him behind Raikkonen and Felipe Massa's Williams, but worse was to come: before his fight back had gathered pace his engine began making unhappy noises and he coasted to a safe place before retiring.
Ironically, as that triggered the Virtual Safety Car while the RB12 was craned away, the deployment effectively scuppered team mate Daniel Ricciardo's chances of pressuring the Mercedes.
Williams and capitalising on opportunities
Losers more by accident than design. With Valtteri Bottas eighth and Felipe Massa ninth on the starting grid, Williams might reasonably have expected to come away with a decent haul of points - but Austin didn't exactly go to plan.
Bottas's race fell apart at the start as he clashed with Nico Hulkenberg in the first corner - the German having been squeezed as Sebastian Vettel again cut in tightly. The result was a puncture and some rear-end damage for the Williams man, who limped back to the pits, then struggled home to a distant 16th place, bruised in the final laps by Felipe Nasr's Sauber.
Massa, meanwhile, made a great start, going round the outside of the melee, and sat pretty in seventh place, ahead of Sainz, until his game got disrupted by the Virtual Safety Car deployment on the 29th lap. That left him to chase after the Spaniard, but while he was waiting on the Toro Rosso's tyres to begin degrading, they were caught by Alonso. Massa was caught out by an opportunistic move from his former team mate - which was made worse by the fact he suffered a puncture in the process. The Brazilian eventually crossed the line in seventh, on a day when fifth was firmly up for grabs.
Force India and the first lap
Nico Hulkenberg and Sergio Perez looked well-poised at the start in Austin, lining up seventh and 11th respectively. The pair ended the first lap 21st and 17th.
Hulkenberg's day indeed ended there: steering arm damage, caused as he was squeezed between Vettel and Bottas, forced him to retire. Perez, meanwhile, lost ground after being tipped into a spin by Daniil Kvyat at Turn 11. He did at least manage to fight back, rescuing eighth at the flag - but like Williams, this was a day when more was possible.