Venus Williams has become the oldest Australian Open women's finalist in professional tennis history after downing CoCo Vandeweghe in three sets.
Turning 37 in June, Williams is chasing a maiden Aussie Open and eighth grand slam title.
Williams will face her sister Serena, or Croatian Mirjana Lucic-Baroni in Saturday night's final.
Should the sisters meet it will be their ninth grand slam final against one another and first since Serena beat Venus at Wimbledon in 2009.
Remarkably, Venus has been battling Srojden's syndrome - a debilitating auto-immune disease that threatened to end her career.
"It's an unbelievable thing to watch Serena Williams play tennis. I would love to be out here and I would more than anything love to see her across the net from me on Saturday," Venus said.
Serena has won the Australian slam six times.