Super Sinner continues perfect ATP Finals run with victory over Medvedev
World number one Sinner had already qualified for the semi-finals thanks to Alex De Minaur winning the opening set in his defeat to Taylor Fritz earlier in the day.
And he only needed a set to ensure top spot in the Ilie Nastase Group and deny Medvedev a place in the last four of the season-ending event in Turin.
Sinner was in no mood to disappoint his passionate home supporters and put in the latest in an increasingly long line of impressive performances to head into the semis with a perfect three wins from three.
"I have a reason to smile, it was a good match and a brilliant atmosphere as always," said a delighted Sinner.
"It was a difficult match, Daniil and I know each other really well so I knew that I had to get it right tactically... Let's see who I have in the semi-finals, I'm happy to get there."
Medvedev would have progressed with a win in straight sets but the world number four has now won just one of his last nine matches with Sinner and was outclassed in northern Italy.
After finishing the season with no titles, he told reporters that he rated his season "zero out of 10" when looking at "where I put my goals and where I finish."
"I want to be number one in the world, but I didn't play well enough this year, by far," Medvedev said.
"I'm No. 4 in the big tennis world. I'm super proud about that because, as I said, especially in the end of the year, I struggled throughout the whole year. Every practice, every match was a struggle for me."
Sinner is hunting his first Finals title after an exceptional season in which he won seven tournaments, including his first Grand Slam victories at the Australian and US Opens.
He lost last year's final to Novak Djokovic, who pulled out of the tournament injured this time around and he entered the 2024 event already assured of becoming the first Italian to top the ATP end-of-year rankings.
However, he has been dogged by controversy after twice testing positive for traces of the steroid clostebol in March.
He was initially cleared by the International Tennis Integrity Agency but at the end of September, the World Anti-Doping Agency appealed, seeking a ban of up to two years.
World number five Fritz joins the man who beat him in the US Open final in the next round after coming from behind to beat De Minaur 5-7, 6-4, 6-3.
On Friday Sinner's big rival Carlos Alcaraz will try to reach the semis when he faces Alexander Zverev.
Wimbledon and French Open champion Alcaraz currently sits third in the John Newcombe Group.