My gut feeling was correct this time. I knew if Djokovic's shoulder was bothering him, Stan will make him suffer and work with the rallies. It's unfortunate that Djokovic had to retire but it is very smart of him to do it. No need to continue playing especially if you are two sets down.
As for Wawrinka, it must be a great feeling for him to finally playing at a high level. When he is confident and fit, he is fun to watch.
One last thing: This is why it will be hard to predict on whether or not Djokovic or Nadal will surpass Federer on the slam's count. There's too many variables that can happen to derail their pursuits. Federer was one point away from winning his 21st slam but Djokovic won the match and title. But right now, Djokovic was force to retire because of a nagging injury. That's why at this point of their careers and age, they need every break and luck they can get so they can maximize their opportunity to win a slam. Because they know deep down, everything can change really quick!