Kerberís improved play continued into set two as she would take a 4-0 lead before taking set two behind a mix of her baseline aggression and several key baseline errors from Williams.
More baseline errors from the American early in set three led to a Kerber 2-0 lead.
Williams cut her errors to take the next three games to take the lead 3-2 before then serving for the match at 5-3.
Kerber broke serve on breakpoint following a Williams crosscourt forehand which landed wide.
Serving to stay in the match, Kerber reached gamepoint before Williams connected with a stunning forehand down the line volley winner to reach the second of five deuces of the game.
Kerber as well saved two match points. However on match point three, Williams took control midway through
the point with a powerful crosscourt forehand which set up a final forehand down the line winner to decide
the match after 2 hours and 25 minutes of play.
"So many matches I've been on the short end of the stick," Williams said. "It felt good this time to pull one out."
In todayís semifinals, Venus Williams faces the 14th seeded Carla Suarez-Navarro of Spain while her sister, the top ranked Serena Williams takes on her good friend and the 11th seeded Caroline Wozniacki of Denmark.
Should both of the Williams sisters win today, they would then compete against each other in Saturdayís semifinals.