MELBOURNE, Australia - Professional tennis is a slippery, fast-evolving species as we discovered again last year when both No. 1-ranked players dramatically lost their crowns at season's end.
Since then, it's been a swirling series of events that have left the ruling hierarchy very much in question.
On the women's side, three former Grand Slam champions all experienced significant turbulence: Petra Kvitova survived a terrifying stabbing incident and could miss six months, Victoria Azarenka gave birth to a son and hopes to return later this year, while Maria Sharapova continues to serve a drug suspension that will end in April.
Thirty-somethings Roger Federer and Rafael Nadal, the greatest players of their generation who both missed Slams after injuries, prepared to test themselves in this disjointed Australian Open. Juan Martin del Potro, another major champion recovering from injury, is also among the missing. So is American Madison Keys, a top-10 player.
"The way this offseason has been going," Mary Carillo, the Tennis Channel broadcaster said recently, "it's hard for me to act like I know what I'm talking about on TV."
In recent years, have there ever been more curious questions going into a season? Famously, the Australian Open is called the "Happy Slam," but under these fairly infamous circumstances that might require a tweak.
Welcome to the "Wacky Slam."
Perhaps it was inevitable the fortnight's first match on Rod Laver Arena would feature a substantial upset. No. 4 seed Simona Halep was bludgeoned Monday by American Shelby Rogers, 6-3, 6-1, only 75 minutes after the tournament had commenced.
Halep complained afterwards of a sore knee. Rogers, a 24-year-old from Charleston, South Carolina, who made a stunning run to the quarterfinals last year at Roland Garros, almost seemed to see it coming.
"It's no surprise to me," Rogers said in her post-match interview. "I have had some tough draws in the slams, so I'm kind of used to that, playing the seeds and playing big matches right off the bat. Yeah, I think I played great today."
The same wasn't necessarily true for world No. 1 Andy Murray, who struggled to defeat Illya Marchenko, 7-5, 7-6 (5), 6-2 in a match that ran 2 hours, 47 minutes on a day when the temperature soared into the 90s.
There is a keen interest developing here in the possible fortunes of the two 35-year-olds who have won more Grand Slam singles titles than any of their peers.
Serena Williams lost her No. 1 ranking to Angelique Kerber when she fell in the semifinals of the US Open to Karolina Pliskova. After more than three months away from the game, Serena looked ragged in her second match in Auckland, falling to Madison Brengle - and hitting 88 unforced errors.
And while the sabbatical was credited to injuries, this was the second straight year the 22-time Grand Slam champion shut it down after losing in the US Open, leaving some to wonder about her state of mind and motivation. She has a dreadful first-round draw Tuesday, opposite unseeded Belinda Bencic, who was a top-10 player a year ago before injuries brought her down.
It's a grave new world for Federer, too, after he missed two Slams for the first time since 1999. The 17-time major winner underwent the first major surgery of his career (left knee) and saw his record streak of 65 consecutive Grand Slams come to an end. Before Monday night's first-round match against Jurgen Melzer, Federer hadn't played an official match since July 8, when he lost to Milos Raonic in the semifinals at Wimbledon.
Federer, ranked at an unfamiliar No. 16, has an interesting draw; after two qualifiers, he would have to beat No. 10 Tomas Berdych in third round, No. 5 Kei Nishikori in the fourth and Murray in the quarters.
And then there's Nadal. He won two clay titles in the spring, but after granting a third-round walkover in Paris because of a left wrist injury, Rafa struggled the rest of the season. He recently announced the addition of former French Open champion Carlos Moya to his team.
Novak Djokovic, who lost his No.1 ranking to Murray, played poorly by his epic standards in the second half of the season. He made a coaching change, too, relieving Boris Becker of his duties. Becker than chided Djokovic for not working hard enough in the second half of the season, raising even more questions.
"Because of the way it's been going lately, you can't really predict what's going to happen," Carillo said. "There's just so little data out there in terms of what we've seen from all these important people."
And that's precisely what makes this Australian Open so compelling.