The second set was very close and that was the toughest part of the match for Djokovic, losing that set will bring him into a more difficult battle and Medvedev will have a chance to beat him but it cannot be denied that Grand Slams and tie breaks are the best part of Djokovic, it is difficult to break his dominance in during the tie break, but Medvedev played very well in that set.
After Medvedev lost the first set and went into the dressing room for a break, he must have gained strength from whatever. The rallies lasted longer and longer and cost Djokovic a lot of energy and he had to take a deep breath more often. But in the tiebreak, he managed to win the last three points in a row and thus also won set 2. I think that underlined his mental strength.
as usual these games provided by Google team are hard as hell 
