Only thing Tomic can use is his slice, if slice won´t bother Isner than Tomic is screwed. His return is bad, he won´t break John, so only he can hope for tie-breaks. And his level here is nothing special, Smyczek was as good as him, only difference was serve-and in this department he will be totally outserved with John. I think if John will break Tomic match is over, otherwise it can go to few tie-breaks, but John should win this match.