Djokovic is very vulnerable from what I've seen of him. On the other hand, both Thiem and Zverev are playing well and have learned to bring it on the biggest stages against the strongest opposition (Thiem against Rafa and Zverev against Wawrinka). The only problem is they're facing each other. If Djokovic faced one of them in SF and the other in F, I think he'd have about a half chance of going down trophyless. Still, I feel a breakthrough in the air (if it can be called that at this point).