KEY POINTS:
Forehand, backhand, top spin, endurance, mobility, court-craft - all important but the key skill for the winner of the Australian Open men's singles crown will be how he deals with the irksome, worrying stabs of self-doubt.
Mental strength is an obvious requirement - yet the "big four" of
world tennis (Rafael Nadal, Roger Federer, Andy Murray and Novak
Djokovic) all have "head" aches to clear as they line up for the season's first grand slam event.
Perhaps the challenges are best expressed in numbers, in this - the 40th anniversary of the opening of the tournament to all players, including professionals.
Roger Federer is thinking of 14 - the number of grand slams he will have accrued if he wins this one; equalling Pete Sampras' all-time record and which will re-kindle calls that Federer is the best of all-time.
Yet there are other numbers in Federer's mind after his horrible 2008 - where he was dumped out of the Australian Open; beaten by Nadal at Wimbledon, his tennis sanctum; lashed by Nadal in that fearful hiding at the French Open where Federer won only four games before he rebounded to win the US Open.
In addition, he has had a run of losses to the rising Scot, Murray, whose win-loss record now stands at 5-2 over Federer, a chilling statistic from a 2008 season which will leave mental scars as the time when Federer began to lose the aura of invincibility.
Murray perhaps said it best when told that Federer had expressed surprise Murray was contesting favouritism with him for the Australian Open.
"The more you play against [Federer] the less fearful you are, you're not scared to win the match. If you're young and you play against the top guys, once you get close to winning you get nervous. Now I don't get nervous and if I play my best tennis I can beat him."
Which he did three times out of four last year. There were extenuating circumstances - Federer's glandular fever and the fact that only a rare, elevated few maintain consistent form throughout their career.
However, it is difficult to remove the notion that 2008 was the year that time stood still for Federer - or, rather, that Federer stood still. Nadal beat him four times out of four to take the world No 1 spot off him.
Here are some other names who beat Federer last year: Mardy Fish, Andy Roddick, Radek Stepanek, Gilles Simon, Ivo Karlovic, James Blake - none of them players who would frighten Federer in his previous pomp.
Even more frighteningly, if you cross-reference all the matches the top 10 in the world have played against each other (as Sydney's Sunday Telegraph did recently), Federer had the worst win-loss record in the top 10 against his fellow top-10ers.
In 20 matches, Federer won 7 but lost 13 for a 35 per cent win ratio or winning only one in three against a top-rated opponent - an annus horribilis indeed. Nadal and Murray
topped the list with 16-10 (61.5 per cent win ratio) and 13-9 respectively (57.1 per cent), with Russia's Nikolai Davydenko next and France's Jo-Wilfried Tsonga at 7-7 and 50 per cent. The rest - Djokovic, Juan Martin del Potro, Simon, Roddick and Blake all lost more than they won but all had a better win ratio than Federer.
Those numbers will also be rattling round in Federer's skull.
How he gets his head around those results and an advancing feeling of vulnerability will dictate how he fares at this Australian Open.
So too will how he copes with the realisation that he may now equal, and perhaps even beat, Sampras' record - but he may only be able to do so by winning one grand slam event a year rather than the multiples he has previously been used to.
Federer will be focusing on numbers like 57 - the number of minutes it took him to dispose of former world No 1 Carlos Moyer at the lead-up Kooyong tournament he won. Federer has the biggest head game of all to play next week.
The number 30 will be a key one for Rafel Nadal - January 30, to be exact. That is the day of the semifinals which is a key "head" ache for Nadal. The world's no 1 player has never been past a semifinal of a hardcourt grand slam event.
Nadal pooh-poohs this, reeling off the vast number of hardcourt tournament wins he has amassed and says he has done so against all of the same players he meets in the majors.
Maybe, but there can be little doubt that this considerable chink in Nadal's considerable armour will weigh heavy on the mind - just as Roland Garros does for Federer, who may now have to get used to the notion that (just like Sampras) he may never win the clay court grand slam event.
Nadal cannot be under-estimated. He is far too rip-snorting, muscular, tenacious and capable of the most searing ground strokes for that. In addition, he is coming off an injury break for tendinitis in his knee and says he feels no pressure even though he is coming into the event a little 'undercooked'.
He has deliberately positioned himself as beginning to climb the hill again; starting from zero; and denying that he is defending anything - not even his stellar 2008.
"I was out of competition for 2 months but have trained hard and hope to find my best level as fast as possible," said Nadal.
"I feel if I find my best tennis I always have a chance to win
important tournaments and hopefully that will start in Australia."
So, after a slow start to this year - including losses to Murray and France's Gael Monfils - he is trying to fly under the radar; making him dangerous indeed as he has a sweet draw.
Meanwhile Scotland's Andy Murray is thinking of 73. It has been 73 years since a Briton (Fred Perry) won a grand slam event. The weight of expectations has landed heavily on his shoulders with his recent win at Qatar and further banishment of Federer.
Murray's rise and rise through the early part of 2009 saw him equal favourite for Melbourne with many bookmakers but the weight of that 73-year drought hangs heavy.
It proved too much when Murray met Federer in the final of the US Open last year. Tellingly, Murray's win-loss stats over Federer include only one grand slam meeting (which the Swiss won).
That is potentially a big mental hurdle but Murray is a phlegmatic character who is less likely to be unaffected - unlike the last great British hope, England's "Tiger" Tim Henman who was derided by the Aussie crowds as being more of a tiger lily.
In the likely absence of an Australian in the final or even in the latter rounds, Murray could find himself adopted by the Melbourne crowd who might never cheer for an Englishman but who could give voice for a player who hails from a country - like the Irish and Welsh - who have had their moments with the English.
Will be focusing on the number 1 rather than 73 - winning his first grand slam event in what seems sure to be a fine career at the top.
This is a Head game of another type. Djokovic comes to Melbourne with only three weeks practice after changing his Wilson racquet for a Head - a potentially form-altering matter.
There have been rumbles that last year's champion has been too busy partying and not practising. The proof will be seen once Melbourne cranks up to full throttle in 40-degree heat.
After he was dumped out of a build-up tournament in Brisbane by promising Latvian Ernests Gulbis, the 21-year-old Serb admitted spending New Year's Eve in Belgrade, rather than honing his game in Australia, may have been wrong.
He also said his leisurely round of golf in Brisbane the day before playing Gulbis had nothing to do with his straight-sets loss.
Loves hardcourt and will try to focus on the number 4 - he has beaten Nadal four times and is 4-2 over Murray. But his tournament may depend on how well he can get his head around his new Head.
SIX OTHERS TO WATCH
France may seem an unlikely source of an Australian Open shock but there are four Frenchmen who could give the locals more of a surprise than finding a brown snake in their socks drawer.
Last year's surprise package and now 6 in the world, Jo-Wilfried Tsonga, tops the list but he withdrew from a warm-up tournament with a back injury last week and is uncertain. If he is fit, he is drawn well and could again advance - and is worth watching for his serve and volley game alone; a dying art these days.
1. Juan Martin del Potro (Argentina)
Built his momentum cleverly during the Heinken Open and displayed surprising court speed, reach and touch to go with a difficult return of serve. He is world No 9, so hardly a bolter but this may be his step up to the big time.
He has drawn well, although due to meet Roger Federer in the quarter-finals.
2. Richard Gasquet (France)
Likes the Australian Open and has one of the sweetest one-handed backhands in the world game. Now down to world No 25, he has been as high as seven. Has big question marks over his mental strength, can lose big matches he is expected to win and his forehand can go missing - but is still only 22.
Missed chunks of 2008, citing injury and burnout but is regarded as one of the best 'natural' tennis players in the world, with much the same amount of talent as Federer. A dangerous giantkiller if his head's on straight. Has beaten all the other Frenchmen in this list in 2009.
3. Gael Monfils (France)
Ranked 13 in the world, this friend of Gasquet's and Tsonga's stands 1.93m and is fast around the court, with a long reach. Can vary between the devastating and the disappointing. In the 2007 Australian Open, hit a winner timed at over 190km/h, thought to be the fastest ever hit.
Beat Marcos Baghdatis that year but not Gasquet. Didn't play Melbourne last year and reached the semifinal of the French Open, the fourth round of the US Open but missed Wimbledon through injury. Building up his hardcourt and grasscourt ability and a danger in the draw.
4. Gilles Simon (France)
The world No 7 twice beat Federer in 2008, also stunning Nadal by beating him in the semifinal of the Madrid Masters, a tournament everyone thought was in Nadal's bag.
Nicknamed 'The Survivor' by the Spanish media for his habit of clinging to matches by his fingernails, surviving match points and then coming back to win, Simon is a tough opponent of the return-everything school. One of only four men ever to beat Roger Federer, Rafael Nadal and Novak Djokovic since they assumed the top three position in world tennis (the others being Andy Roddick, Andy Murray and David Nalbandian).
5. Marat Safin (Russia)
Powerful, moody, of dubious temperament and mental strength but the big Russian was the champion in 2005 and has the ability to beat anyone on his day - and not only beat them; embarrass them.
His formidable ability to self-destruct and injury worries - including a shoulder problem which may affect him in Melbourne - have meant that ability has been little seen lately and he has been rather left behind by the Federer-Nadal-Djokovic-Murray bandwagon. Still only 28 and down to 27 in the world rankings, Safin was a semifinalist at Wimbledon last year in spite of grass being his least favoured surface. Could meet Federer as early as the third round.
6. Marin Cilic
A Croatian giant (1.98m tall), this 20-year-old has quietly reached No 20 in the world and likes hardcourt. Reached the fourth round in this event last year, taking out two seeds, the fourth round of Wimbledon and the third round of the US Open, losing to Djokovic.
A big server, his game is suited to Melbourne and he started 2009 the right way, winning the ATP tournament in Chennai, India. Scalps last year included Andy Roddick, Fernando Verdasco and Robredo but might need more experience yet.