Only Federer left as Djokovich retires hurt and Murray can't beat Query on one leg. Hard to see beyond Federer right now.From what I've seen so far the Big 4 won't be ripe for the taking this year. And if I was going to pick a dark horse it certainly wouldn't be Delpo - he's not mobile enough and apparently his wrist still bothers him. I didn't see much of Raonic's match but in the little I did see I wasn't impressed. If anybody's going to break through the Big 4 I'd go with Zverev.