(CNN) The Williams sisters were unheard of schoolgirls in the Los Angeles suburb of Compton when their father Richard, a man with no previous experience in tennis coaching, wrote an 85-page plan for his daughters.

Those 85 pages were a strategy for greatness, for fame and fortune.

Venus and Serena, who meet in Saturday's Australian Open final, would revolutionize the sport, the Louisiana native proclaimed. They would become the world's top two players, he predicted.

Not that anyone expected their father's unorthodox blueprint to develop into one of sport's greatest stories.

"Everyone thought he was crazy," Nick Bollettieri, renowned coach of many a grand slam champion, once said.

Serena (L) celebrates with sister Venus (R) and father Richard (C) after beating Steffi Graf in a 1999 final.

After reaching her eighth Australian Open final this week, Serena offered an insight into how her father's vision helped create a dynasty that has dominated the women's game for nearly two decades.

His big innovation was teaching the sisters techniques no one else was trying.

"People were like, 'What are you doing? That's not the right way,'" Serena recalled of those early days in Compton.

"We were definitely able to revolutionize a lot of things in the game. We were able to come out here and just be two really strong women standing up for everything we believed in."

Serena and Venus with their mother Oracene in 1999.

New beginning

The sisters have both topped the women's rankings -- in 2002 Venus became the first African American player to be a tennis No. 1 , and Serena followed her that same year.

And they have been under the spotlight of grand slam finals before, of course.

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There was a time when all-Williams finals were a regular feature in the tennis calendar. But this Australian Open final feels different. It is an unexpected flashback to a different age, a contest to savor.

Though both great champions have been defiant against Father Time, and neither has mentioned retirement, the siblings are in the final chapters of their remarkable careers.

Saturday's final could be their last together at this stage of a grand slam and, as Serena herself has admitted, it is an extraordinary tale.

"This is something that I couldn't write a better ending," the 35-year-old said of the match in which she could finally win an Open-Era record 23rd grand slams.

"This is a great opportunity for us to start our new beginning."

With a combined age of 71, the all-Williams clash will be the oldest grand slam final in the Open Era.

'It's a win-win situation'

Victory would place Serena in history's gap between Steffi Graf (22 major titles) and Margaret Court (24) and return her to the world's No. 1 ranking.

At the other side of the net, however, will be older sister Venus, a seven-time grand slam champion and a 36-year-old whose later career has been hampered by an incurable auto-immune disorder.

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In 2011 she was diagnosed with Sjogren's Syndrome, which causes fatigue and joint pain. It is a major reason for her recent absence from grand slam finals, with her last being in 2009 at Wimbledon.

Serena has predicted Saturday's match, their ninth grand slam final battle but first for almost eight years, will be "uncomfortable," but the six-time Melbourne champion is relaxed whatever the outcome.

"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 explained.

"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 Williams won her first Australian Open title by beating sister Venus in the final in 2003.

'I can compete against the odds'

The sisters -- owners of 29 major singles titles between them, plus 14 together in doubles -- have been the dominant forces in women's tennis for almost two decades and, in this tournament, have been as commanding as they once were in the early part of this century.

Serena has returned to form after an extended break at the end of last year.

She has not dropped a set in Melbourne and, having dominated her rivalry with Venus -- Serena holds a 16-11 record and has won six of their past seven grand slam finals -- the world No. 2 is favorite to triumph for a seventh time Down Under.

"When I'm playing on the court with her, I think I'm playing the best competitor in the game," said Venus, who lost to Serena in her only other Australian Open final in 2003.

"I don't think I'm chump change, either. I can compete against any odds. No matter what, I get out there and I compete.

"I know that it won't be easy. 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. It's wonderful."