In the third set, it seemed that Serena had fully recovered from a back ailment. Both women were serving well, hitting great groundstrokes. Many of the rallies were long standoffs.
However, the game-changer was that Sloane was very comfortable and adept at coming to the net. She had a great feel for her approach shots, they varied each time depending on the situation. She backed it up with effective and professional volleys.
Sloane was able to apply the pressure at these pivotal moments in the match. She forced Serena into numerous passing shot errors. In fact, I do not remember one successful passing shot in the third set by Serena.
Sloane Stephens has the complete package.