The return of Maria Sharapova, Kim Clijsters and Justine Henin to the Australian Open has added even more spice to a women's tournament already overflowing with talent.

There is always an element of mystery attached to the first Grand Slam of the year but the reappearance of the three former world number ones has ensured this year's tournament will be one of the most open in years.

Serena Williams is the favourite and understandably so. She is the current world number one, the defending champion and one of the few players who thrive in the scorching Australian summer heat.

Williams has won at Melbourne Park four times but if she is to make it five she will have to interrupt a winning sequence that has seen her take the title in alternate years since 2003.

"This is what I was born to do," she said. "It's what I do best. "I'm just super mentally tough, I feel like that's definitely one of my strengths."

The American's fighting spirit is unquestioned but she will need to be at her very best to win a fifth title at Melbourne Park.

It is no surprise that she has flagged her older sister Venus as her biggest threat but the Russians and Belgians present a more formidable challenge.

The Australian Open was the last of the Grand Slams to be captured by a Russian woman but they have weight of numbers this year.

Three of the world's top five are Russian and there are five in the top 15 including Sharapova, who has dropped back to 14 after a shoulder injury that prevented her from defending the Australian Open title she won in 2008.

Sharapova struggled to find her best form when she returned to the circuit late last season but the early signs this year are far more encouraging, beating Venus Williams and Denmark's U.S. Open finalist Caroline Wozniacki in recent exhibition matches.

Dinara Safina, the world number two and sister of 2005 men's champion Marat, made the Australian Open final last year.

She also made the French Open final for the second time in a row but her nerves have let her down and she is still chasing her first Grand Slam title.

She has also been troubled by back pain and her early form has been mixed, losing in the quarter-finals of the Sydney International, but she insists she is ready.

"I'm looking forward for Australia. If I was not fit, I would not come here," she said. "It makes no sense if you're not top fit to come."

Her loss to Serena Williams at last year's Australian Open final was brutal but if there was any consolation in her defeat at the French Open, it was that she lost to compatriot Svetlana Kuznetsova, the current world number three.

Kuznetsova was eliminated in the second round at Sydney, though she too remains unfazed.

"I'm not coming in the best shape ... but I'm not worried," she said. "It's gonna depend on how I develop during the tournament (but) if I can manage to construct every match well, I may have a good chance."

One Russian woman who has been in great form is Elena Dementieva, the 2008 Beijing Olympics champion, ranked fifth in the world but still chasing her first Grand Slam after reaching the French and US Open finals in 2004.

However, the most intriguing twist is the return of the Belgian pair, Clijsters and Henin, who played each other in the 2004 Australian Open final.

Clijsters retired in 2007 to start a family, and Henin a year later because she was sick of tennis, but neither could resist coming back.

Clijsters made a fairytale return to the sport when she won the U.S. Open for the second time, beating Serena Williams in the semi-finals when the American was disqualified for abusing a lineswoman.

Inspired by what Clijsters achieved, Henin announced she was also rejoining the circuit and played her first tournament in Brisbane this month.

As fate would have it, she met Clijsters in the final and the pair produced a classic that served as a perfect appetiser for the Australian Open.

"I think we set the bar pretty high for ourselves for the rest of the year," said Clijsters, who beat Henin in a three-set thriller.