I disagree with the notion that Stan only won AO14 due to Rafa’s injury. Stan was already up a set and a break before Rafa started hitting 80 mph first serves.
I noticed something was wrong with Rafa early in the 1st Set actually, because Rafa kept hitting balls far over the baseline continuously, very strange unforced errors that I've never seen before from him.
It was because he was standing very upright, unable to move his back properly
Rafa had stiffness early in the match, and pain later in the match, so he only served slow when the pain arrived and that slow serving made Wawrinka lose rhythm (also because Rafa wasn't putting any top spin on groundstrokes) and Rafa won the 3rd Set.....and then in the 4th Set Rafa's painkiller kicked in, and he served faster but Wawrinka found rhythm and won.
Wawrinka had played very close sets with Rafa in the past, so Rafa's back problem was easily enough to put Wawrinka over the top.
While Rafa's back problem clearly wasn't the only reason why Wawrinka won, I think there was a decent chance Rafa would have won if healthy, but either way it would have been close.....probably a 5-setter.