I don't know which direction it will go but I'm sure it will be 5 sets because Cilic does that a lot against young players (this the guy who played Nishikori for 5 hours in a heat wave here) and Harrison knows this is winnable. I picked Cilic in the poll but it's a coin flip.
This is one of those matches that I'd probably want to bet on the underdog either way. Gun to my head I think that Cilic puts a few more balls in play and grinds Harrison down, but I wouldn't be surprised to see it go either way.
As crazy as it sounds, this is one of those rare matches that I would give almost an equal chance to all six options, as both are capable of being great or erratic enough for either one of them to win in straights or either one of them to win 3 sets to 2. There's no result between these two that would come as a "shocker," as they say.
If Cilic brings his A game then he should win but he does that very rarely these days so Ryan has a real chance of upsetting a seeded Croat for the second year running. It's hard to understand what happened to Cilic who hasn't been a threat at a slam since last year's Australian Open.