Serena won , 6 - 4 , 6 - 3 , on the way to the title .
The last time the Williams sisters played each other was at the round of 16 at Wimbledon in July .
Williams won , 6 - 4 , 6 - 3 , on the way to the title .
The last time the Williams sisters played each other was at the round of 16 at Wimbledon in July .