Top-seeded world number one Williams overpowered Russian left-hander Ekaterina Makarova 6-1 6-3, unleashing her daunting firepower against the 17th-seeded Russian.
Wozniacki advanced when China's Peng Shuai broke down in scary distress due to heat illness and retired in the second set, while trailing 7-6(1) 4-3.
The results delivered on a pre-tournament wish made by the buddies, who each entered the event longing for a victory to ease personal frustrations.
"She's a good friend of mine," said former world number one Wozniacki, whose gaping hole in her resume remains the lack of a grand slam title.
"We were saying when the tournament started, 'We're in separate sides of the drawing, so hopefully we can meet in the finals. It would be great if that were to happen.'"
Williams said she had the same thought when the draw was made.
"She obviously wants to win and go for her first grand slam, and I want to win and try to make a little history," said Williams, who wants to end a disappointing grand slam season on a happy note by claiming her 18th slam singles to tie Chris Evert and Martina Navratilova for fourth on the all-time list.

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