Serena Williams anticipates a battle against her "toughest opponent" after booking a spot in the Australian Open final opposite sister Venus.

After Venus had overcome unseeded surprise package Coco Vandeweghe in three sets, Serena reached her eighth final in Melbourne with a 6-2 6-1 destruction of Mirjana Lucic-Baroni.

Serena leads the head-to-head record against her older sister 16-11 and has won six of the grand-slam finals they have contested against each other - including Venus' last run to a slam showpiece at Wimbledon in 2009.

"She's my toughest opponent, no-one has ever beaten me as much as Venus has," Serena said on-court.

"She has a pretty good record against me. No matter what happens we've won, she's been through a lot, I've been through a lot.

"To see her do so well it's great so I look forward to it. A Williams is going to win this tournament."

Serena said that battle lines will not be drawn between the pair before Saturday's showdown.

"No, we definitely talk," she said at a news conference. 

"I think now more so than anything. Nothing can break our family. If anything, this will definitely bring us closer together, knowing that I want to see her do the best that she can possibly do. I know that she definitely wants to see me do the best that I can do.

"I really do feel like we'll both be happy for each other no matter what happens. But still we want to be able to go out there and play our best. We'll probably both be watching each other's matches."

Venus had not dropped a set before falling behind to Vandeweghe - conqueror of reigning champion and world number one Angelique Kerber - and the elder Williams believes she is in form to trouble her sister.

She said: "I probably just need to continue playing like I'm playing. I haven't played badly. I lost a set today. I was not happy about it. But my opponent deserved that set. So what else could I do? Try to get the next two.

"I will try to do the same.

"When I'm playing on the court with [Serena], I think I'm playing the best competitor in the game. I don't think I'm chump change either, you know. I can compete against any odds. No matter what, I get out there and I compete."