The latest battle between the world's two dominant men's players had all the feel of another major championship final, but in front of his own adoring fans in Turin, the Italian world No.2 won the day with his glorious Sunday best 7-6 (7-4) 7-5.
To cap a season in which they shared the four grand slam crowns, the end-of-term decider between the pair was another spectacular, close-fought duel, but though Alcaraz has wrestled back the top ranking, it's Sinner who showed again why he's the king of the indoor arenas.
This, amazingly, was his 31st straight victory on indoor hard courts, a record that stretches back two years to when he lost the final of this event to Novak Djokovic.
But to finish a year when he also had to serve a ban for a doping offence following his Melbourne triumph and before going on to win at Wimbledon, it clearly meant everything to Sinner to prevail in front of his home fans as he threw himself to the floor in joy after the two-and-a-quarter hour classic.
"Celebrating this trophy at the end of the year after such an intense last couple of months, there's no better ending for the season for me," said the 24-year-old, who joins a list of the sport's greats as a back-to-back season-ending championship winner.
Djokovic, Roger Federer, Australian Lleyton Hewitt, Pete Sampras, John McEnroe, Ivan Lendl, Bjorn Borg and Ilie Nastase all achieved the feat previously.
"It was a very, very tough and close match-up but I'm very, very happy how I handled the situation and it means the world to me. Against Carlos you have to be at your very best."
Sinner certainly was, taking the title without conceding a set. Having not dropped his serve all week, including in his semi-final triumph over Australian No.1 Alex de Minaur, Alcaraz was at least able to say he finally cracked his delivery.
Still, that was not enough.
Sinner saved a set point at 5-6 in the first stanza with a big second serve, and then played a blinding tiebreaker.
Alcaraz needed his right thigh to be treated by a trainer on a couple of occasions and had the injury wrapped after the first set, but he was still able to then earn the break that nobody else had been able to achieve all week in the opening game of the second set.
Sinner, though, responded to claw it back to 3-3. Still, Alcaraz had a chance to break again in the next game but he mishit a forehand, and Sinner survived to pile on the pressure in the 12th game, finally clinching victory when his rival sent a backhand wide.
Alcaraz had no complaints about his defeat, telling his conqueror at the presentation ceremony: "I'm really happy with the level that I played today, with the performance. I just played against someone that hasn't lost a match on an indoor court since two years.
"I hope you're going to be ready for next year because I will be ready. Hopefully, playing more finals against you."
Indeed, it has set up the prospect of yet another early-season duel perfectly at Melbourne Park, the only grand slam that Alcaraz, with six titles to his name, has yet to win.
In the earlier doubles final, Harri Heliovaara and Henry Patten were crowned season's champions by defeating Joe Salisbury and Neal Skupski 7-5 6-3.
