Venus Williams beat Coco Vandeweghe at the Australian Open to reach her first Grand Slam final for eight years.
The 36-year-old fought back to see off her fellow American 6-7 (3-7) 6-2 6-3 in Melbourne, setting up a potential final against her sister Serena.
Venus Williams, seeded 13th, lost to her sister in her only previous Australian Open final 14 years ago.
Serena Williams plays unseeded Croat Mirjana Lucic-Baroni in the second semi-final.
A victory for the world number two would set up the ninth all-Williams final at a Grand Slam - the last of which, at Wimbledon in 2009, was Venus's most recent major singles final.
"It is unbelievable to watch Serena play tennis - the way she hits the ball and the competitor she is," said Venus Williams.
"It would be a dream to see her on the opposite side of the net on Saturday."
Venus grabs 'moment in the sun'
Vandeweghe, 25, had played superbly in seeing off world number one Angelique Kerber and French Open champion Garbine Muguruza to reach the last four, but she could not maintain that level in the semi-final.
The world number 35 deservedly took the first set on a tie-break but it was the experience of Williams that eventually prevailed.
Williams converted four of five break points, but more importantly reduced Vandeweghe to just one from 13 as the younger American was reduced to throwing her racquet in frustration as the chances slipped by.
Two double faults handed Williams a decisive double break in the second set and the seven-time Grand Slam champion broke again at the start of the third.
Vandeweghe stayed close enough to keep the pressure on, saving three match points before finally cracking with an error on the fourth, prompting a jubilant twirl of celebration from Williams.
"Everyone has their moment in the sun. Maybe mine has gone on a little longer than other people, but I have nothing else to do," joked Williams - BBC
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