Melbourne:Men's tennis has moved swiftly from one dominant player to two, then the Big Three and now the Big Four, making this year's Australian Open the least predictable in recent history.
World number one Rafael Nadal is seeded top, Novak Djokovic is defending champion but Britain's Andy Murray is some bookies' favourite, rankling three-time winner Roger Federer.
"Murray's the favourite? Good for him, but it doesn't help him a lot," said the Swiss.
Federer heads into the season's opening Grand Slam without the top seeding for the first time since 2004 but encouraged by his US Open win in September.
The Swiss also lifted the Kooyong Classic trophy on Saturday as he goes in search of Grand Slam title number 14, which would equal the record set by Pete Sampras.
"I'm playing well, I'm feeling well," he said. "It's going to be interesting. I think it's an interesting year ahead of us. That's why I'm excited."
However, Federer has already lost twice this year to Murray, whose red-hot form is raising genuine hopes that he may be about to end Britain's 73-year wait for a Grand Slam title.
Murray has also smashed past Nadal and defended his Qatar Open title in a rip-roaring start to the year after dominating the latter part of last season.
"I'm going into each match confident, not as many nerves," Murray said.
"In the past I've been a little bit erratic with my performances. I feel like now I've sort of become more consistent. That's made a big difference."
Murray's physical fragility may be a worry in the 128-man draw, often played in brutal heat, after a back problem flared during the Doha semis. He was also a first-round loser last year to eventual runner-up Jo-Wilfried Tsonga.
"I feel good going into the Australian Open but after what happened last year I don't want to get too carried away," he said.
Meanwhile, Nadal has made a slow start to the only season he has begun as world number one, going down to the in-form Gael Monfils in Doha after his loss to Murray at an exhibition event.
The Spaniard, who took an extended break at the end of last year with chronic knee tendinitis, admits he is lacking match practice as he looks to improve on last year's semi-final appearance.
"You never know, no? Hopefully yes," he said, when asked if he was ready for the Open. "But I was two months out of competition, so maybe I need a few more matches to get my rhythm."
Djokovic is breathing down Federer's neck for the second ranking but also has made an unedifying start to the season.
The Serb blamed a change of racquet after losing to Ernests Gulbis in Doha, and was then ousted in the Sydney International semis by Finland's Jarkko Nieminen.
"(My game's) not 100 percent, but it's getting there," Djokovic said.
Sixth-ranked Tsonga dazzled Melbourne with his run to the final last year, but his build-up has been hit by a back injury which forced him out of the Sydney International.
Czech player Radek Stepanek is buoyed by his Brisbane International win over Spaniard Fernando Verdasco, while Marin Cilic was victorious in Chennai and ex-number one Lleyton Hewitt may be a dangerous floater on home soil.
Federer opens his campaign on Monday against Andreas Seppi while Djokovic is playing Andrea Stoppini. On Tuesday, Nadal faces Christophe Rochus and Murray plays Andrei Pavel.