You probably knew that by now.
But here are five things you might have missed over the past week at the year-end championships in London.
Tipsarevic: Djokovic can rule the world
Janko Tipsarevic is good buddies with Djokovic, so it's to be expected that Tipsarevic thinks highly of his fellow Serb and Davis Cup teammate.
What can Djokovic achieve in 2013? Whatever he wants, according to Tipsy.
Although he ended the season by topping Federer, Djokovic lost the No. 1 ranking for a time and nabbed one major compared to three in 2011.
"Last year was something special," Tipsarevic said. "I'm not going to say it's never going to happen because this sport is full of surprises. But to be honest, I was expecting him to stay No. 1 because just talking to this guy, maybe this is a little bit too personal, but in my opinion on his mind is only one thing -- to be the best and No. 1 in the world forever and ever and ever.
"I wouldn't be surprised if he stays No. 1 all throughout next year and wins whatever he has in his mind, like more Grand Slams, French Open, all four."
Janko, a reminder: The last man to win all four in a season was Rod Laver in 1969.
More time for exhibitions
Players complain about the grueling 10.5-month schedule -- then they take part in exhibitions in November and December, often embarking on long journeys.
But with the ATP chopping two weeks off the tennis calendar this year, Federer said it makes sense. The Swiss will be displaying his silky skills in South America, like Djokovic.
"That's the beauty of an offseason," Federer said. "You're allowed to do whatever the hell you want. I think that's what's nice, instead of having such a congested space where you just can barely take enough rest. Now if players want to play some matches, wherever it may be, that's their choice. If you want to rest for six weeks, just don't do anything, you can do that as well, which was not possible in the past."
Federer plans to take a two-week holiday before his maiden trip as a professional to South America.
Following a tennis and soccer exhibition in Brazil in the next week -- also featuring Gustavo Kuerten -- Djokovic will take 2.5 weeks off "in a very tropical, very beautiful place with no racket, no tennis, no nothing."
The season is over for Andy Murray, but not the worry. He's fretting about what to get coach and laconic eight-time Grand Slam winner Ivan Lendl for Christmas.
"What do you buy Ivan Lendl for Christmas?" Murray asked the BBC. "A sense of humor, maybe? Only joking! Ivan has helped me a lot this year. Working with him is one of the best decisions I've made in my career, and I know he'll keep pushing me hard to achieve even more. We'll be meeting up in Florida for my winter training block next month, so I'd better stay on his good side!"
Murray added that he'll be spending Christmas in the U.K. for the first time in four years.
Rafa not forgotten
Djokovic and Murray met three times since the start of the U.S. Open in August, and all three were punishing contests that went the distance. But at the beginning of 2012, Djokovic versus Rafael Nadal was the pre-eminent men's rivalry in tennis.
Djokovic extended his winning streak to seven against Nadal in the Australian Open final only for the Spaniard to win the next three.
Rafa's knees intervened, and he's been on the sideline for five months.
"Tennis misses Rafa a lot," Djokovic said. "He's a globally recognized tennis player and athlete, very popular, very attractive player to watch and a great competitor. He already became a legend of this sport, and he's only 26. I really hope for him that he's going to recover and we're going to see him in Australia [in January], because he definitely deserves to be back."
Fed feels for Ferrer
When del Potro beat Federer to clinch a spot in the semifinals -- Federer had already advanced -- the nightcap resembled a so-called Davis Cup dead rubber.
Ferrer, usually not one to complain, wasn't pleased, especially because he defeated Tipsarevic to finish the round robin at 2-1, like del Potro.
"I talk yesterday with the ATP, and I express my opinion, no?" Ferrer said. "My opinion: I will have to play the first match."
He had Federer's sympathy.
"I really wanted to give him a chance and give myself the best possible preparation for the semis, really hoped I could win. Not that I prefer David over Juan Martin, no, not at all," Federer said. "But more disappointed for [Ferrer] than I am about losing today, to be quite honest."
Still, it was a positive week for Ferrer and Spain. Apart from Ferrer, Marcel Granollers and Marc Lopez won the doubles title. Ideal preparation for this weekend's Davis Cup final at the Czech Republic.