America's Williams sisters can write another chapter in their eventful family history as they attempt to set up their ninth Grand Slam final, eight years after the last, at the Australian Open on Thursday.

In a plot straight from the 2000s, both sisters have raced into the Melbourne semifinals without a dropping a set, and they appear equally focused on getting their hands on the title.

At least one American is guaranteed to be in Saturday's decider, with Venus confronting confident compatriot Coco Vandeweghe in their last-four clash on Rod Laver Arena.

Following them on court will be Serena against fellow former teenage prodigy Mirjana Lucic-Baroni, who is into her first Grand Slam semifinal in 18 years.

It has become a tournament of the golden oldies, with Venus 36, Serena 35 and Lucic-Baroni 34. Vandeweghe at 25 is the young pretender.

Serena said it was a testament to the Williams' staying power that they were still fighting for titles at their age.

"I've been doing this for many years. The past few years I've been super-consistent," she said. "But yeah, I'm just really happy for Venus, obviously. She's doing amazing.

"I'm really happy for Mirjana, as well. I was there when she first started. To see her be able to never give up actually is super-inspiring to me. It's a wonderful story."

Few would have picked a Serena-Venus final as the tournament got underway, but it is now a 50-50 chance.

They last met in a major decider at Wimbledon in 2009, which Serena won. The younger Williams has the clear edge, winning six of their eight Grand Slam final encounters stretching back to the US Open in 2001.

Venus said she was not interested in the past, only the future and the immediate threat posed by the aggressive Vandeweghe.

"Anything that's happened before is just so. I'm ready for the future, if I can be honest," she said.

"I have a lot to give. I have a lot to give to the game. I feel like I have a lot of great tennis in me. I have nothing to lose, literally."

Vandeweghe is a major threat to an all-Williams final.

She demolished French Open champion Garbine Muguruza in a blitz of big hitting to make her first Australian semi, and she is supremely confident to boot.

"It's amazing to be in a semifinal. But, you know, not satisfying," said Vandeweghe, who also stunned world number one Angelique Kerber in round four.