Djokovic vs Casper Ruud.- I'll probably go win under on this match, under 22.5 as this might be just 2 sets for Djokovic to win.
Tsitsipas vs Rublev - this one could be interesting, Tsitsipas slightly favourite, but I will go with the over 22.5.
under22.5 for Djokovic is risky, it is a first match, and I would not be surprised to see him let down first set, to win second and third, after all it is group stage, and he can let even a win, to qualify for next stage
regarding Tsitsipas and Rublev, over should come, even without third set, with one tie-break
regarding whole tournament, I would be surprised to see Djokovic not taking it in the end