He had a cake draw though.
Washed up, injured Davydenko. Home-crowd favorite, and thus choking Tomic. Broken-foot Raonic. No wonder he's through.
If he faced Isner, he'd get pushed all the way. When you've got a serve like that, you can make things happen the good old-fashioned way - force a couple of breakers, and a few points could swing it.