It is eight years since the American sisters, who have a combined age of 71 and 29 slam titles between them, last faced each other across the net for one of the sport's four major prizes.
Younger sister Serena was at her brutal best on Rod Laver Arena as she brought an end to the dream run of Mirjana Lucic-Baroni at Melbourne Park, thrashing the 34-year-old Croatian 6-2 6-1.
Venus, 36, had a much tougher time and needed to draw on the experience of 73 grand slam campaigns to rally from a set down for a 6-7(3) 6-2 6-3 victory over compatriot Coco Vandeweghe.
Serena, who beat Venus in her older sister's only previous Australian Open final in 2003, does not expect sentiment to play a role in Saturday's title-decider either, but Thursday was all about family pride.
"For us both to be in the final is the biggest dream come true," the 35-year-old Californian.
"She's my toughest opponent, no one has ever beaten me as much as Venus has. I just feel like no matter what's happened we've both won.
"It is definitely 100 percent the best-case scenario that I could have ever dreamt of."
FAIRYTALE
While Serena was finding her feet after four months out with a shoulder injury and Venus has ended a eight-year grand slam final drought, Lucic-Baroni's fairytale return from years in the tennis wilderness trumped them both.
A doubles champion at Melbourne Park as a 15-year-old, Lucic-Baroni's career went into a tailspin on the back of trauma in her personal life before she battled back to reach Thursday's semi-final as world number 79.
Her left leg heavily strapped, she came out firing winners as if her life depended on it but was simply unable to stay with the world number two in the 50-minute contest.
The six-times champion was all but untouchable when her first serve hit the mark and she sealed the win when Lucic-Baroni smashed a forehand into the net, reaching her 29th grand slam final where she will bid for a 23rd major title.
Serena gave her opponent a huge hug at the net before watching on smiling as Lucic-Baroni took a selfie as a memento of her day in the sun.
"Honestly she's an inspiration, she deserves all the credit today," said Serena.
Lucic-Baroni offered "zero excuses" for her defeat and said she had been overwhelmed by the messages of support she had received.
"I felt like the whole world is with me and supporting me, sharing this really amazing moment with me," she said. "It's really filled my heart with so much joy."
Venus needed almost three times as long to overcome world number 35 Vandeweghe, who broke the 13th seed on her first service game and won the opening set on a tiebreaker.
CLUTCH POINTS
The big-hitting 25-year-old's hopes had rested on the accuracy of her serve and booming winners but her challenge faded as the unforced error count racked up and her first serve success rate hovered around the 55 percent mark.
The key to seven-times major champion Venus's victory, though, was her ability to raise her game at decisive moments and she saved 12 of 13 break points she faced, seven in the second set alone.
Venus danced around the court in breathless delight at her victory and gave the crowd an elaborate version of her traditional twirl, having ensured she would become the oldest Australian Open finalist in the professional era.
"Everyone has their moment in the sun," Venus added. "Maybe mine has gone on a while but I'd like to keep that going. I got nothing else to do."
Vandeweghe was visibly upset at losing her first grand slam semi-final, indulging in a "feel-sorry-for-myself moment", as she described it.
"But you have to give credit where credit's due," she said. "My opponent played better than I did today when it mattered, in the clutch points."
(Editing by Amlan Chakraborty and John Stonestreet)
