By Nick Mulvenney
SYDNEY, Jan 12 (Reuters) - With even their main rivals trumpeting Novak Djokovic and Serena Williams as the runaway favourites to win the Australian Open, it is tempting to view the honour roll at the year's first tennis grand slam as pre-ordained.
However well the pair are playing, they should perhaps bear in mind that the brutal heat, inspired opponents and the heartbreak of injury have unseated more than a few 'sure things' over the years at Melbourne Park.
Djokovic has been backed by no less than Roger Federer to achieve what even the Swiss was unable to do in his pomp by winning three successive Australian Open titles.
The Serbian world number one loves the hot conditions and a playing surface that brings the ball to him high and slow, and has won three of his five majors in Australia.
The conditions favour the fittest and there are few fitter than Djokovic as he proved last year when he beat Andy Murray in five sets in the semi-finals and then prevailed against Rafa Nadal in the longest-ever grand-slam final.
Nadal's battered body means he is absent this year, leaving Djokovic in the top half of a draw with the less-than-imposing figure of David Ferrer standing as his toughest opponent should both reach the semi-finals.
Murray and Federer are in the other half of the draw and, perhaps for the first time, the Scot is more favoured than the 17-times grand slam champion after finally entering the club of major champions at last year's U.S. Open.
Having also ended Britain's long drought without a grand-slam champion, and won an Olympic gold medal on home soil to boot, Murray should be freed of the pressure that contributed to his defeats in the Melbourne finals of 2010 and 2011.
Federer, four-times a champion in Australia, cannot be considered a spent force quite yet, particularly after the 31-year-old's remarkable renaissance at Wimbledon last year which allowed him to briefly recapture the number one ranking.
Spain's Ferrer, who enjoyed his best year on the tour in 2012, and Czech Tomas Berdych would be better bets as dark horses were they not in the same half of the draw as Djokovic.
Sixth seed Juan Martin del Potro has a good draw and has recovered physically from the wrist injury that almost ended his career in 2010.
However, the tall Argentine has yet to reproduce the form that won him the 2009 U.S. Open at another grand slam and has failed to get beyond the quarter-finals at any of the four majors since his comeback.
Williams is an overwhelming favourite for a sixth women's title after storming back to pre-eminence last year with titles at Wimbledon and the U.S. Open.
The 31-year-old has won 35 of her last 36 matches and is odds on with the bookmakers to take home a third successive grand-slam title and a 16th in all.
Victoria Azarenka is the defending champion but the world number one has such a wretched record against the American (1-11) that their potential meeting in the semi-finals would present a major mental hurdle for the Belarussian.
Azarenka started last year on fire, going 26 matches unbeaten, but this year a freak injury resulting from a pedicure forced her to withdraw from her semi-final against Williams at the Brisbane warm-up.
The 23-year-old said at Friday's draw that the damaged toe was now okay and she was happy with her preparations for her first grand-slam title defence.
Maria Sharapova, the 2008 champion, was humbled by Azarenka in last year's final and also forced to withdraw from Brisbane with a collar-bone problem.
The Russian also declared herself fit and well to compete in Melbourne on Friday and, seeded second, ended up in the other half of the draw from Williams and Azarenka.
Apart from Williams, the other form player at the start of this year has been fourth seed Agnieszka Radwanska, who put together a winning streak of nine matches to win back-to-back titles at the Auckland and Sydney warm-ups.
The Pole, beaten in the Wimbledon final by Williams last year, will arrive in Melbourne bursting with confidence that her all-court guile might enable her to beat more powerful opponents.
China's Li Na, a finalist in Melbourne in 2011 before her French Open triumph later that year, is always a threat if she can hold her equilibrium and is also in form after winning her first tournament of the year in Shenzhen.
The Australian Open is now the richest tennis tournament in the world with a prize purse of A$30 million ($31.70 million) and the days when it was considered the least of the four grand slams and threw up more than its fair share of surprise champions are gone.
So if Djokovic does match Andre Agassi and Federer as the only four-times men's singles champions in the open era, and Williams equals Margaret Court's open-era record with a sixth women's crown, few will be greatly surprised.
The championships begin on Monday. (Editing by Clare Fallon)