Federer's season began in promising fashion, having reached the semifinals at January's Australian Open. But it went downhill from there for the much-loved Swiss record-breaker.
The 17-time grand slam winner injured his knee while running a bath for his twin daughters, necessitating surgery for the first time in his career. He subsequently missed the French Open with a back complaint -- the first major he bypassed since 1999 -- and shut down his season after re-injuring the knee at Wimbledon in July. At No. 16, the 35-year-old finishes 2016 outside the top 10 for the first time since 2001.
Djokovic makes history
Novak Djokovic didn't end his season the way it began, as he saw his two-year reign as the men's No. 1 come to an end. But Djokovic flourished in the first half of 2016.
When the Serb beat Andy Murray in June's French Open final, he became the first man since Rod Laver in 1969 to win four consecutive majors. The enormity of Djokovic's accomplishment wasn't lost on Murray, who said at Roland Garros: "It's not happened for an extremely long time and will take a long time to happen again."
Murray emulates trio
Back in June, it appeared as if Murray would never usurp his fellow "Big Four" members. And while his haul of three majors still significantly trails Djokovic, Federer and Rafael Nadal, the Scot did emulate them by finishing the year as the men's No. 1
-- the first time since 2003 one of the trio wasn't atop the year-end standings.
Murray enters 2017 on a 24-match, five-tournament winning streak. He, too, became the first tennis player to win back-to-back singles gold medals at the Olympics
Kerber's slam breakthrough
Serena Williams is used to winning multiple majors in a season -- she has done it seven times in a remarkable career. But another female player achieving the feat in recent times is extremely rare, which makes Angelique Kerber's titles at the Australian Open and US Open even more impressive.
Not including Williams -- who tied Steffi Graf's Open Era record off 22 majors by downing Kerber at Wimbledon -- Justine Henin was previously the last female player to claim at least two majors in a season, in 2007.
Sharapova's drug ban
For the first time in nearly 15 years, Maria Sharapova won't have a year-end ranking. The Russian -- who for most of the past decade has been the richest female athlete in the world -- officially dropped out of the rankings in October after not competing in enough tournaments in the previous 52 weeks.
That, of course, is because of the drug ban Sharapova was handed in June. Her two-year suspension was later reduced to 15 months. meaning the five-time grand slam champion is eligible to return in April.
Team title for Argentina
The losing finalist four times prior to 2016, Argentina's drought in the Davis Cup is no longer thanks in large part to Juan Martin del Potro, easily tennis' comeback player of the year. Del Potro -- after losing to Murray in a gripping Olympic final in Rio -- upset Murray in the Davis Cup semifinals and won both his singles matches in the final, rallying from two sets down to begin Argentina's comeback in Zagreb, Croatia.
The Czech Republic also came back from 2-1 down on the road in the Fed Cup final against France in Strasbourg to claim a fifth title in the last six seasons, the most successful spell in the women's team event since the US won seven consecutive trophies from 1976 and 1982.