Men's professional tennis was only slightly less volatile than the stock market in 2008.
Consider the striking change at the top, as Rafael Nadal, all of 22 years old, won two Grand Slam finals against Roger Federer, who had held the No. 1 ranking for more than four years. There was the swift ascension of Andy Murray to the No. 4 ranking, just behind Novak Djokovic, and the expansion of the Big Three into the Big Four. And then there was the explosive introduction of Jo-Wilfried Tsonga, 20-year-old Argentine Juan Martin Del Potro and Gilles Simon into the top 10.
In fact, the current top 10 features five players who weren't there at the end of 2007. Tsonga and Del Potro both climbed an impressive 36 rankings spots.
Federer finally ran into an opponent he could not defeat -- he contracted mononucleosis early in the season -- and never fully recovered his movement, or his mojo. His string of 10 consecutive Grand Slam finals was snapped in Australia and, heading into the season-ending Tennis Masters Cup tournament next week in Shanghai, Federer has his worst won-loss record -- an extremely mortal 65-14 -- since he's been No. 1. The funny thing? With Nadal (injured right knee) out of the mix in Shanghai, Federer is the top seed.
Two weeks ago at his hometown tournament in Basel, Switzerland, the subject of his former No. 1 ranking came up. Federer's answer was instructive and reminiscent of Pete Sampras toward the end of his career.
"Obviously, I have points to defend here and in Shanghai, but that's not what my life's about anymore," Federer said. "It's about winning titles. Often you're on the tour and you go week by week and you're like, 'Oh my God, I've got quarterfinal points to defend from last year,' but now when I come into a Grand Slam I don't care if I have 1,000 points to defend or 50.
"I know the rankings are still an important factor, but really it's about winning titles, being healthy and enjoying the tour."
Federer, now 27, gathered himself down the stretch of the season, won an Olympic gold medal in doubles and then -- when many had counted him out -- hoisted the U.S. Open trophy for the fifth consecutive time.
"In some ways, Federer might be the biggest story of the year -- and not the struggles, but the ultimate success at the Open," longtime pro Todd Martin said recently from his Florida home, where he is resting in between senior events. "For the first time in his career, since establishing himself as the best, he faced a significant amount of adversity.
"All his winning has been done so smoothly and seemingly effortlessly. You haven't seen him sweat. But he looked vulnerable consistently throughout the year. This year, you saw him sweat.
"Still, he got that one Grand Slam and, going forward, that changes everything."
Paul Annacone, coach of men's tennis for the Lawn Tennis Association and the British Davis Cup coach, feels the adversity may serve Federer well in 2009.
"This is the first year Roger actually has to get better, which is scary, but great," Annacone said. "To see Rafa beat him in two finals and wrestle the No. 1 ranking away from him, well, it's a great time for him to reassess and adjust."
Below Federer and Nadal, there has been some dramatic movement in the rankings. While Tsonga, Del Potro and Simon made the largest jumps among high-ranked players, the most impressive rise belongs to Murray. He moved from outside the top 10 (No. 11) to No. 4, claiming some of the toughest real estate in sport.
Still only 21, Murray could conceivably close in on Djokovic at No. 3 in January, since Djokovic is the defending champion at the Australian Open, where Djokovic won his first career Grand Slam. Murray is still looking for his first major after losing to Federer in the U.S. Open final.
Annacone, with his LTA ties, watched with a professional interest as Murray proceeded to his first major final in New York.
"For a 21-year-old to look so comfortable -- he was never out of his comfort zone against Roger," Annacone said. "He didn't feel he had to do anything crazily different to succeed. The kid has a lot of self-belief and is clearly focused.
"He came back and beat Roger in Madrid. I'll be more surprised if he doesn't continue to get better. There's no reason Andy's not going to be knocking on the door again. I'll be surprised if he's not holding one of the majors trophies really soon."
Martin, too, appreciates the leap Murray made this year.
"The word that comes to my mind is transformation," Martin said. "He's transformed himself from the [whiniest] kid on a bank of 100 courts to somebody who looks happy playing tennis. He's channeled some of that energy into a positive, and if you can channel the energy you have positively, you're in a better position to compete."
With Nadal defending both his French Open and Wimbledon crowns, it is not impossible to imagine a happy, healthy Federer reclaiming the No. 1 ranking, even though that is not his stated goal. As with Sampras in his later years, the issue is likely to be more mental than physical.
"As long as the win in New York doesn't make him comfortable," Martin said, "I think he's got every reason in the world to be tremendously motivated to grind it out in November and December and be ready for Australia.
"If things go well in Australia, we could be on the verge of another two, three Grand Slams in a year. The matchup he struggles with the most [Nadal] has the least likelihood of happening in Australia and New York. That happens to be where Roger matches up pretty well with the rest of the field."
Greg Garber is a senior writer for ESPN.com.