Impossible to predict, so I will try to do exactly that.
The main reason being Zverev. Dude is just unbelievable moody and he can go from total clowning to unplayable and back very fast and with no warning. His FH seems to improve and became a weapon, of course not as good as his opponent, but not a liability. BH is fantastic and if he was able to execute a coherent plan, he should pepper Tsitsipas worse side until it breaks. And it will break eventually as it always does.
So, from Tsitsipas point of view, he should take every chance to dictate with FH. Actually, I think he should be more aggressive than he is from that wing. I have a feeling that in today's coaching a lot of emphasis is put on percentages and "margins", restricting people with serious talent. We would never see Fed's FH today as it would be marked as too risky. So, go full Shapovalov and unleash it Stefanos.
I'll go with Tsitsipas in 4. Day time conditions are probably ideal for Tsitsipas to beat Zverev, and Tsitsipas has had a tougher draw than Zverev so far, so the former should be more battle ready than Zverev is.
I think Zverev would win this in 5 sets. Zverev is playing really well -- won a lot of 6-1 sets -- and his serve is getting him a lot of free points. I think Tsitsipas is also playing really well, but I feel Zverev's serve will give him the edge.