Sinner collapsed to the ground with a mixture of joy and relief after sealing his triumph at the season-ending tournament where he hasn't lost a match since being beaten in the 2023 final by Novak Djokovic.
Alcaraz has won four of his five meetings with Sinner this season, all of which have been in finals of top-level tournaments -- with two deciding Grand Slams.
The five-time Grand Slam champion made it two wins from two in the Jimmy Connors Group with a comeback 6-7 (2/7), 7-5, 6-3 victory over last year's runner-up Fritz in Turin.
Sinner, who lost last year's final to Novak Djokovic, did not put a foot wrong this time round as he finished undefeated and without dropping a set to earn $4,881,500 in prize money.
Sinner barely gave Ruud time to breathe as he rattled off the first three games and took the first set in half an hour, before sweeping to a comprehensive victory.
Fifth-ranked Fritz triumphed 6-3, 3-6, 7-6 (7/3) over world number two Zverev in a thrilling match at the season-ending event in Turin.
Serbia are one of the eight surviving nations from September's group phase and will face Britain on Thursday.
At 36 years old Djokovic is still tennis' number one player by some distance and he has racked up a host of new records this season, taking his Grand Slam tally to 24 and finishing top of the year-end world rankings for the eighth time.
Novak Djokovic closed in on a record-breaking seventh ATP Finals title on Saturday after sweeping past Carlos Alcaraz 6-3, 6-2 in a dominating semi-final display he hailed as his best of the tournament.
Serbia are one of the eight surviving nations from September's group phase and will face Britain on Thursday.
At 36 years old Djokovic is still tennis' number one player by some distance and he has racked up a host of new records this season, taking his Grand Slam tally to 24 and finishing top of the year-end world rankings for the eighth time.
Novak Djokovic closed in on a record-breaking seventh ATP Finals title on Saturday after sweeping past Carlos Alcaraz 6-3, 6-2 in a dominating semi-final display he hailed as his best of the tournament.
Novak Djokovic had enough of an edge at the beginning and the end as he beat Stefanos Tsitsipas 6-4, 7-6 (7/4) on Monday in the ATP Finals, a defeat that ended the Greek's hopes of finishing the year at number one.
