Zverev battles from set down to beat Alcaraz in ATP Finals opener
Germany's Zverev, a two-time winner at the year-ending tournament, put on a powerful display to see off world number two Alcaraz who is not on top form after returning from injury at the end of last month.
Wimbledon champion Alcaraz struggled with lower back and left foot problems which had kept him out of action since the Shanghai Masters in early October.
He was then dumped out early at the Paris Masters by Russian qualifier Roman Safiullin and flagged towards the end of a bruising contest with giant German Zverev, the number seven seed in Turin.
Zverev is tough opposition on hard courts like the one at the Pala Alpitour and made full use of his height and power to see off Alcaraz and take the lead in the Red Group.
The 26-year-old rattled off 16 aces and was only broken once over the course of an impressive win in which he hit more winners and made significantly fewer unforced errors than out-of-sorts Alcaraz.
"Against Carlos I'm not somebody who's going to win a lot of baseline rallies so I knew that I had to serve well, to hit a lot of aces, I knew that I had to make a make a lot of first serves... it paid off in the end," said Zverev.
Alcaraz claimed the first set after breaking back to love in game six to level at 3-3 and took the lead in the next game after saving three break points.
Zverev overpowers Alcaraz
The set was then taken to a tie-break when Zverev saved three set points on his own serve in game 12, but Alcaraz's class shone through to claim a set which lasted well over an hour.
Zverev bounced back though and rattled off three games in a row to set up a straightforward second-set victory as Alcaraz was rocked back by his opponent's service game.
And Zverev pushed on to claim the honours, sealing the win in trademark style with two whopping serves which Alcaraz - who had been at advantage - simply couldn't handle.
Before Zverev's win, Novak Djokovic was presented with the trophy for finishing the season as world number one, a position he secured after winning his thrilling Green Group opener with Holger Rune on Sunday night, a match which lasted more than three hours.
Djokovic is the red-hot favourite to claim his seventh Finals title which would put him out of his own as the record winner, one ahead of retired great and old rival Roger Federer.
"It's obviously the crown of the season, finishing the year as number one in the world I think is a dream of every tennis player, it's one of the most difficult things to do in our sport," said Djokovic on court.
"Winning Grand Slams and being number one in the world are probably the pinnacles of the sport. It's been a very long year for all the players and to be able to stand here is a blessing."
Later on Monday 2020 champion Daniil Medvedev faces fellow Russian Andrey Rublev in the day's other Red Group match.
