by John O'Donovan

Serena Williams starts as overwhelming favourite to win the Australian Open for a sixth time and her 18th Grand Slam. 

Williams is coming off the back of an incredible year when she won 11 tournaments and 78 of the 82 matches in which she played. However, one of her four defeats came in the Australian Open to Sloane Stephens.

Victoria Azarenka went on to win in Melbourne for the second consecutive year and the defending champion will surely provide the biggest threat to the American. 

The Belarusian also has the confidence gained from two victories over the American last year.  

Other challengers will include Maria Sharapova, Li Na and Agnieszka Radwanska, while there are a host of exciting young players to watch such as Stephens, Laura Robson, Eugenie Bouchard and Simona Halep. 

The younger Williams is the greatest player of this generation and arguably the best of all time. No female player has ever hit the ball harder while her serve is also unsurpassed.

The simple fact of the matter is that if Williams plays her best tennis she will win the tournament.

She appears to be playing close to her best and is on a run of 22 matches unbeaten including beating Azarenka in straight sets to win in Brisbane last week, where she also beat Sharapova in the semi-final.  

However, there is hope for the rest of the field. Two of those four defeats last year came in grand slam events, where she lost to Stephens in the quarter-final of the Australian and against Sabine Lisicki in the fourth round at Wimbledon.

Both of these women were ranked outside the top 20 at the time, showing that she can sometimes suffer shock losses. Her two other defeats came at the hands of Azarenka in Cincinnati and in Doha, meaning the Belarusian beat her twice on hard courts in 2013 .  

Azarenka is the player most likely to challenge Serena for the title. She won two of their four battles last year and is the only player who can match the American’s consistency and power.

Her return somewhat neutralizes the Serena serve, and she can hit winners from anywhere on the court.

She goes into the matches against Williams with confidence and a plan, and it is paying off although she needs to beat her in a grand slam to prove she is a serious challenger to the world number one as Serena has won all eight of their encounters in slams.

However, Azarenka did not finish 2013 in good form and is not playing like the second best player in the world at the moment.

The fact that she reached the final in Brisbane last week cannot disguise that she is in poor form. She won only one match in her final six tournament matches last year.

It started with her loss to Serena in the US Open decider and ended with her disappointing showing at the WTA Championships in Turkey in October.

Despite this, she has won the Aussie Open for the last two years, so must be considered a legitimate contender.

Maria Sharapova is third seed but it is very hard to see her winning a fifth grand slam. 

Her semi-final defeat to Williams last week in Brisbane, against whom she trails 15-2 in their head to head and has not beaten in nine years, was her first tournament since August as a result of a shoulder injury.

After reaching the French Open final, she lost to qualifier Michelle Larcher de Brito in the second round at Wimbledon and to Sloane Stephens in the first round at Cincinnati in what was her last match of 2013.
However, Sharapova is one of the toughest competitors in the sport and is one of only 10 women who have won all four slams so she cannot be dismissed. 

Her problem will be should she play Williams, her powerful game which leaves most players floundering, appears ordinary against the American.  For the Russian to beat her, she will have to play at the very peak of her powers and hope that Serena suffers a serious off day.

Li Na is, perhaps, the biggest threat to Williams and Azarenka. Na is a two-time finalist in Melbourne including last year where a lapse in concentration and an injury ensured a three-set defeat to Azarenka. 

She reached the quarter-finals at Wimbledon, semi-finals at the US Open and the final of WTA End of Season Championships where she lost to Serena in three sets.

She has begun this season well winning the Shenzhen Open last week. The Chinese player is a definite dark horse for the title.

Agnieszka Radwanska is another player who will consider herself a contender for the championships.  She had a very consistent 2013 reaching the quarter-finals or better in three of the four grand slams and suffered a heart breaking semi-final Wimbledon defeat to Sabine Lisicki.

She has also started this season well winning all three of her matches in The Hopman Cup last week.  The world number four is the least powerful player in the WTA top tier, but she has a great tennis brain and peerless anticipation.  

By changing pace, spin and direction frequently, she has found a way to succeed without the relentless power game favoured by so many players.

Petra Kvitova has never built on her Wimbledon 2011 triumph and has had a disappointing time since, although she did show a return to form towards the end of last year winning the Pan Pacific Ocean and reaching the last four of the WTA Tour Championships.  

She is also, on her day, one of the few players who can match Williams for fire power as the left-hander has one of the best serves in tennis, can hit winners from anywhere on the court and knows how to volley.  

Sloane Stephens is a player many people believe has an outside chance of winning the tournament. The 20-year-old American had a breakthrough year in 2013 defeating Williams in the Australian Open in the process of reaching the semi-finals while she also reached the quarter-finals at Wimbledon and the fourth round at the other two slams.

It will also be exciting to watch how some of the young players fare in the tournament such as WTA Newcomer of the Year Eugenie Bouchard and Simona Halep

Another player to watch out for is Romania's Sorana Cirstea who finished last season very strongly.

Britain’s Laura Robson has suffered a slump since her excellent performance in Wimbledon and is now ranked 46th in the world.

However, she is a dangerous opponent and none of the seeds would enjoy playing her in the early rounds.  She pulled out of a warm-up event in Hobart with a wrist injury, but it is thought she will be fit for the Open.

It will be fascinating to see if Caroline Wozniacki’s recent engagement to Rory McIlroy will see an improvement in her form.

She finished 2010 and 2011 as number one in the World but ended last year clinging on to the number ten spot.  It is hard to believe she is only 23, making her the youngest player in the top ten. 

She has not started the year well, losing in Sydney this week to Lucie Safarova in the second round in straight sets.

Two other players to follow are Venus Williams and Ana Ivanovic who played in the final in Auckland last week with the Serbian winning in three tight sets.  

Both are former world number ones and have shown a return to form of late.

All things considered, it is impossible to look beyond Serena Williams to win the title.  She knows that her best is simply too good for everyone else and now at 32 she is showing a mature and calm approach to the game.

This means that barring injury or a slump in form, it will take a superb performance from one of the aforementioned women, with Azarenka the most likely candidate, to prevent the American from becoming the 2014 Australian Open champion.