Serena Williams faces the unpalatable prospect of handing over the world No.1 ranking to long-time rival Maria Sharapova if she loses to Dominika Cibulkova in the Australian Open quarter-finals on Wednesday.

Williams – who has spent the last 101 weeks atop the rankings – will drop to No.2 if she is unable to find a way past the feisty Slovakian and Sharapova also makes it through to the final at Melbourne Park.

But the American will start as the red-hot favourite against Cibulkova, last year’s Open runner-up, who has taken only one set off Williams in four previous meetings.

“She is a really good player,” said Williams, a five-time Australian Open champion chasing her first title at Melbourne Park since 2010.

“To be her size, she hits it so hard and plays so well.

“She’s just such a powerful, compact, great player.

“I just have to stay focused and not under-estimate her.

“She actually almost beat me before so I want to make sure I come ready and prepared.”

For her part, Cibulkova is thrilled to be starting the year well again, just as she did in 2014 when she made it all the way to her first major final before losing to Li Na.

“Even for the big names, it’s not easy to defend something like this so I don’t think like that,” said the No.11 seed from Slovakia.

“It’s a new year. It’s a new start.

“I’m starting the year pretty well again.

“So this is how I see it – it’s the beginning of the year so I always feel fresh.”

Sharapova last headed the world rankings for a brief four-week period in mid-2012, but it is Williams who has owned top spot for the past two years.

The American also owns undisputed head-to-head bragging rights, having won her last 15 matches against Sharapova dating back a full decade.

Sharapova plays fellow Russian Ekaterina Makarova in the semis on Thursday ahead of a potential showdown in the final against Williams.

HOW SERENA WILLIAMS AND DOMINIKA CIBULKOVA MATCH UP FOR THEIR AUSTRALIAN OPEN QUARTER-FINAL CLASH AT MELBOURNE PARK ON WEDNESDAY:

1-SERENA WILLIAMS (USA) leads 11-DOMINIKA CIBULKOVA (SVK) 4-0

2010 Wimbledon, grass, R32, Williams 6-0 7-5

2013 Miami, hard, R16, Williams 2-6 6-4 6-2

2013 Rome, clay, R16, Williams 6-0 6-1

2014 Brisbane, hard, QF, Williams 6-3 6-3

SERENA WILLIAMS (USA)

Age: 33

Ranking: 1

Career-high ranking: 1 (2002)

Plays: right-handed (two-handed backhand)

Career prize money: $US63,500,799 ($A68.71 million)

Career titles: 64

Grand slam titles: 18 (Australian Open 2003, 2005, 2007, 2009, 2010; French Open 2002, 2013; Wimbledon 2002-03, 2009-10, 2012; US Open 1999, 2002, 2008, 2012-2014)

Australian Open win-loss record: 65-9

Best Australian Open performances: champion 2003, 2005, 2007, 2009, 2010

DOMINIKA CIBULKOVA

Age: 25

Ranking: 10

Career-high ranking: 10 (2014)

Plays: right-handed (two-handed backhand)

Career prize money: $US6,281,247 ($A7.93 million)

Career titles: 4

Grand slam titles: 0

Australian Open win-loss record: 17-7

Best Australian Open performance: finalist 2014