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.
The opening semi-final produced some scary moments as China's Peng fell victim to the severe conditions during an energy-draining, groundstroke battle with Wozniacki.
The match was still very much in doubt with Wozniacki serving at 4-3 and facing break point when the unseeded Peng suddenly grabbed her thighs and stumbled to the back wall of the centre court with what appeared to be severe cramping.
In obvious distress, the 28-year-old doubles specialist was eventually helped off the court to be evaluated by doctors.
A valiant Peng, playing her first career grand slam singles semi-final, refused to quit and returned in 11 minutes after a medical examination.
Six points later, Peng curled up in agony on the baseline, and officials called the match and Peng was lifted into a wheelchair and taken from the court to a standing ovation after the abbreviated two hour four minute battle.
Williams, the two-times defending champion, came on the centre court next and seemed determined to spend as little time as possible in the heat and succeeded, trouncing Makarova in 60 minutes.
The American blasted 24 winners, including five aces. Makarova hit six.
Makarova, playing in her first slam singles semi-final, praised the victor. "Serena, she's a great, unbelievable player. Today she was so aggressive."
Friendship will be set aside in Sunday's final between the players who earlier this year spent a beach holiday together in Miami with some serious chips on the line.
Image: Serena Williams of the United States celebrates winning match-point against Ekaterina Makarova of Russia during their semi-final at the 2014 U.S. Open in New York.
Photograph: Adam Hunger
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