World number one Sinner is bidding to retain his title at the prestigious end-of-season tournament and he cruised into the semi-finals in front of a delighted crowd in Turin.
The 24-year-old was not at his best and struggled with a hand problem at the start of the match, but still had more than enough to see off Zverev for the fifth straight time.
"I've known Sasha for a long time now and we changed our tactics a bit today. Fortunately, I only needed a break in each set to win. I'm very happy obviously, let's see how we go in the next match," said Sinner on court.
"I've played well in recent weeks so I came into the tournament feeling good. We want to go as far as possible but also to play the right way."
Zverev hasn't beaten Sinner since the 2023 US Open, being destroyed by the Italian in the semi-finals of the recent Paris Masters, and again, the German couldn't handle the four-time Grand Slam champion.
Sinner was brutal on his serve, rattling in 12 aces, and once he took the first set with his third break point of game 10 he never looked back.
Zverev needed to win in straight sets to book his place in the semis but will now have to beat Felix Auger-Aliassime, a 4-6, 7-6 (7), 7-5 winner over Ben Shelton, in his final group match on Friday in order to progress.
But he cut an irritated figure on court, frustrated by his inability to capitalise on any of his seven break points, a series of unforced forehand errors and at one point by a flashing advertising sign.
Sinner meanwhile will take on Shelton aiming to top the group and set up a clash with whoever finishes second in the Jimmy Connors Group, which is currently led by his great rival Carlos Alcaraz.