Surely winning the tie breaker in the first set was important, but I thought that Medvedev won't come back from that as this is sometimes his weakness and he often plays as if he gave up mentally. But this time he won the second set and I thought this could be the turning point in the match as the number of unforced errors went up for Sinner as well and Medvedev made use of his chances. Still though both Sinner and Medvedev aren't the most stable players on the tour, so it was open against after the game was tied in the second set. Yet he deserved the win I think.
The first set when Sinner managed to win through a tie break I thought the same as you that it would not be possible for Medvedev to come back and take the second set, but apparently he was able to but in the third set Sinner took it to become champion.It's true that Medvedev isn't the most consistent player, but compared to others like Rune, Ruud, and Tsitsipas, he's a pretty consistent player, it's quite rare for him to lose in the early rounds of the tournament, but in the Paris Masters this time I doubt he'll make it far away because the tournament schedule is too close, and Djokovic and Alcaraz have the opportunity to repeat the Cincinnati and US Open finals
Medvedev is now already at the Paris Masters, the last exciting tournament of the year. Djokovic and Alcaraz are both there and then in about 2 months we'll know whether Nadal can make it true and play the Australian Open again. Hopefully it's going to happen.
There is no certainty that he will play at the Australian Open, indeed he has returned to training but in several interviews he is not sure about his body condition but because there are still around two months left, there will probably be many changes including finally him being fit to play in the first Grand Slam in 2024 
