tomic looks to be improving now. if i was forced to make a prediction, i would say tomic but he has to return just well enough to secure a few break points in each set. he does not need to return well in every single isner service game obviously.
absent that and it is isner`s match.
tiebreak time is isner time so that needs to be avoided.
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.
If Isner's serve is on, I think he has the advantage. IMO, Tomic tends to struggle with big hitters and Isner likes to attack the 2nd serve (Tomic needs to serve well to avoid the pressure). I think Isner in 3.