Whenever one of the four major tennis tournaments comes across the calendar, time can be separated into two realms: B.D.–Before the Draw–and A.D., otherwise known as After the Draw. We therefore begin a preview of the 2009 Australian Open by looking at the men’s field in the “B.D. era.”

Without seeing any brackets, it can already be said that one of the keys to this year’s tournament is a player who won’t be competing Down Under. Amazingly enough, it’s the last man you’d expect to miss a two-week tournament.

Nikolay Davydenko has been the iron man of the ATP tour over the past four years, playing more tournaments than any other top-10 player in three of the past four seasons. While it’s true that logging too many matches and catching too many plane flights have probably prevented Davydenko from being fresh for the later rounds of slams, the Russian has remained a fixture in the upper reaches of his sport, finishing each of the past four seasons in the top 5.

Davydenko’s absence from the Australian Open is significant not because the man nicknamed “Kolya” is a top-tier slam contender, but because this dogged competitor can be counted on to give opponents a grinding match in the round of 16 or the quarterfinals. In the heat of an Australian summer, Davydenko is the kind of opponent no one wants to face: You might beat him, but your body–in the later rounds of a slam–is likely to pay a price and suffer in subsequent rounds.

So as the tennis world awaits the announcement of the 128-player draw for the Aussie Open, all eyes won’t necessarily be on Davydenko, but they will focus on the spot vacated by Kolya. Four people will be particularly interested in seeing how the draw stacks up, particularly in the quarterfinals: Rafael Nadal, Roger Federer, Novak Djokovic, and Andy Murray.

It’s not exactly a secret that the men who comprise the Big Four will tower over the rest of the field in Melbourne Park. Nadal, Federer, Djokovic and Murray represent four formidable forces, and one can make a very strong case for each person’s chances in Australia.

Nadal is, quite simply, the reigning No. 1 and a great player coming off a career year. Nadal reached the semifinals at each of last year’s hardcourt majors (the Australian and U.S. Opens), and seems poised to reach a hardcourt slam final as long as his body holds up. Nadal’s tennis has become increasingly overpowering, to the point that the surface in question is becoming less important with each passing year… and each passing shot produced by Rafa’s signature forehand. As long as his fitness doesn’t deteriorate, Rafa will be heard from in this and every other tournament he enters.

Federer suffered a back injury at the very end of his 2008 season, but the Swiss superstar appears healthy and unconcerned about a recent pair of losses to Andy Murray in the Middle East (Abu Dhabi and Doha). After claiming his 13th career slam at the U.S. Open last September, there should be no questions about Federer’s confidence. Murray is becoming a thorn in Roger’s side, but the former No. 1 hasn’t lost to the Scot in a best-of-five match, and that reality can’t be discounted. Federer has problems with Nadal, but not on hardcourts, and the Swiss took a stand against Djokovic in last year’s U.S. Open semifinals. As long as Federer doesn’t encounter a repeat of the mononucleosis that sapped his energy during last year’s Aussie Open, he’ll be able to contend for his 14th major title, which would tie Pete Sampras’s coveted record.

Djokovic might have lost his own Aussie Open tune-up to the rising young Latvian, Ernests Gulbis, but the Serbian superstar has every opportunity to defend his championship, won last year in a terrific four-setter over the aforementioned Tsonga. Djokovic possesses plenty of stamina and abundant willpower, but the fiery competitor learned in 2008 that it’s a lot harder to be the hunted, and not the hunter. Once Djokovic bagged his first slam title, the tour attacked him with a greater sense of urgency, and the pressure of staying one step ahead caught up with him in the second half of the season. A shocking second-round loss to Marat Safin at Wimbledon, and a bizarre series of incidents at the U.S. Open–especially a mini-meltdown in a pair of on-court interviews during the second week of the tournament–revealed a player who was mentally exhausted. Djokovic didn’t do much of anything during the fall indoor season, but he regrouped to win the Tennis Masters Cup in Shanghai. If Djokovic is mentally fresh in Australia, he could certainly repeat. There are questions concerning his mind, but not his well-rounded tennis, built on a foundation of airtight defense.

Murray is the one member of the Big Four who lacks a slam title, but very few members of the global tennis cognoscenti expect that drought to continue for very long. Murray announced his emergence last year with his first Masters Series titles and his first grand slam final, a straight-set loss to Federer in New York. After dusting off his Swiss foe twice in the past few weeks, Murray now possesses an extra amount of comfort against Federer, which will come in handy if the two men meet in a semifinal or final. A year ago, Murray was still a bit in awe of Nadal and Federer. Today, that’s no longer the case. Murray’s body and mind have both ripened to a considerable degree; an Australian Open championship would only confirm an ascendancy that has already taken flight.

Nadal. Federer. Djokovic. Murray. Four men have a relatively equal chance at a prestigious crown in Melbourne. They’ll all be looking for the cushy quarterfinal draw that would propel them onward, with minimal cost to their physical endurance levels. The Big Four stand atop their sport, but they’re all wondering how the absence of No. 5–a man named Nikolay Davydenko–will impact their fortunes at the 2009 Australian Open.