Serena Williams is on the cusp of making Grand Slam history, 19 years after her first appearance at the Australian Open -- with only her greatest rival, sister Venus, able to stop her.

The 35-year-old American made her Grand Slam debut in Melbourne way back in 1998 and won the first of her major titles at the US Open a year later.

She has since accumulated 22 over an astonishing career, matching Steffi Graf's Open-era record. One more on Saturday -- her seventh in Australia -- and she will hold the record outright, with only Margaret Court's all-time mark of 24 left to achieve.

Williams has refused to talk about the possibility of finally surpassing the German, after intense pressure over the long-standing record took its toll at last year's US Open, when she lost in the semi-finals.

But she now has a golden chance of further cementing her place in history, and at the same time reclaiming the top world ranking that Angelique Kerber seized from her last year.

"It is what it is. Like I said from the beginning, I don't really talk about that any more," Serena said when pressed on what breaking the Graf record would mean.

Intriguingly, it is her older sister who could ruin her day, with Venus, 36, turning back the clock to make her first Grand Slam final since Wimbledon in 2009.

It was Venus who knocked Serena out in round two on her Grand Slam debut 19 years ago, and they have since played eight major finals against each other.

Serena leads 6-2 in those finals, and has an overall 16-11 win-loss record against her sibling.

While reluctant to speak about making history, she is happy to dwell on another all-Williams final, heaping praise on Venus.

The elder Williams has beaten injuries and overcome Sjogren's syndrome, a rare, energy-sapping autoimmune disorder, to reach a 15th Grand Slam final, nearly eight years after her last.

"After everything that Venus has been through with her illness and stuff, I just can't help but feel like it's a win-win situation for me," she said. 

"I was there for the whole time. We lived together. I know what she went through. 

"It's the one time that I really genuinely feel like no matter what happens, I can't lose, she can't lose. It's going to be a great situation."

Serena said she never lost hope of meeting her sister again in a major final.

"This probably is the moment of our careers so far," she said. 

"I never lost hope of us being able to play each other in a final, although it was hard because we're usually on the same side of the draw."

Venus, who has won seven Grand Slam finals and lost another seven, will be the oldest finalist at Melbourne Park in the Open era, joining a select list of 30-somethings including Chris Evert, Martina Navratilova and her sister.

The 13th seed also takes the record for the longest wait between major finals, at seven-and-a-half years since her last appearance at Wimbledon in 2009.

Venus admits her sister doesn't have many weaknesses in her game to exploit, but she is up for the challenge.

"When I'm playing on the court with her, I think I'm playing the best competitor in the game. I don't think I'm chump change either, you know," she said. 

"I can compete against any odds. No matter what, I get out there and I compete.

"So it's like two players who really, really can compete, then also they can play tennis." 

"Okay, it won't be an easy match," she added. "You have to control yourself, then you also have to hopefully put your opponent in a box. This opponent is your sister, and she's super-awesome."