Serena Williams returned to No. 1 and earned $12.3 million in prize money this year. (Ronald Martinez/Getty Images)
Here's a look at some of the numbers that defined the year in tennis. Click here for our complete archive of year-in-review posts.
0: American men who reached the fourth round at any of the four Grand Slam tournaments.
1: Title for Roger Federer, who before 2013 had won at least three every year since 2002.
3: Consecutive Australian Open titles for Novak Djokovic, a record in the Open era (since 1968). The third came in 2013.
4: Female players in the Open era who have won all four majors at least twice: Serena Williams (who accomplished the feat with her French Open title), Steffi Graf, Martina Navratilova and Chris Evert.
6: Titles for Simona Halep, second most on the WTA Tour, behind Williams' 11. Halep had none entering 2013.
7: Aces for seventh-ranked Sara Errani. Williams led the tour with 480.
8: French Open titles for Rafael Nadal, the first man to win that many titles at any Grand Slam tournament. The eighth came in June.
9: Singles retirements/walkovers in the second round of Wimbledon, equaling the most in any round in a major in the Open era. Seven came on Day 3, believed to be a single-day record.
11: Years between Williams' first WTA Player of the Year award, in 2002, and her most recent one, in 2013. That's a WTA record.
12: Years between Grand Slam semifinal appearances for WTA U.S. teens. Sloane Stephens made the semifinals of the Australian Open this year as a 19-year-old; Serena Williams reached the 2001 U.S. Open final as a 19-year-old, losing to her sister Venus.
13: Match points Tommy Haas needed to outlast John Isner 7-5, 7-6 (4), 4-6, 6-7 (10), 10-8 in the third round of the French Open. Isner saved nine match points alone in the 12th game of the fourth set.
14: Consecutive Grand Slam semifinals for Djokovic, second all time behind Federer’s 23.
16:ATP titles won by players 30 or older, the most since 1975.
17: Years between victories at the Australian Open for 42-year-old Kimiko Date-Krumm, who won an opening-round match for the first time since 1996. (Date-Krumm didn’t compete from 1997-2008.) She became the oldest woman to win a singles match in tournament history. Date-Krumm lost in the third round.
24: Consecutive victories for Djokovic to end the season, the longest such streak since Federer won 29 in a row to finish 2006.
31: Williams' age when she reclaimed the top ranking in February, making her the oldest women's No. 1. (She turned 32 in September.)
34: Consecutive victories for Williams, a career-high streak that started in the second round of the Sony Open in March and ended in the fourth round of Wimbledon in July.
36: Federer’s record streak of major quarterfinals, which ended at the All England Club. The longest active streak now belongs to Djokovic, with 18.
47: Grand Slam appearances for Marion Bartoli before winning one, a WTA record. Bartoli became the sixth woman in the Open era to win Wimbledon without dropping a set.
70: Points played in a first-set tiebreaker by Benjamin Balleret and Guillaume Couillard in a qualifying match for a Futures tournament in Plantation, Fla. Balleret won 36-34.
71: Shots in the longest rally of the Australian Open, between Gael Monfils and Gilles Simon in the third round. In fact, the two Frenchmen had the five longest rallies in Melbourne, all 42 strokes or more.
77: Years since Great Britain produced a Wimbledon men's champion before Andy Murray halted the drought in July.
1912: The last time, before this year, that no American men made the third round of Wimbledon.
1927: The last time, before this year, that a player came back from two sets down to win three consecutive Grand Slam matches. Tommy Robredo accomplished the feat this year at the French Open, and Henri Cochet did it 86 years ago at Wimbledon.
979: Aces for Isner, who led the ATP Tour for the third time in four years. (He averaged 16 per match.) Milos Raonic was second, with 883, in the same number of matches as Isner.
112: Rankings spots jumped by WTA Newcomer of the Year Eugenie Bouchard, 19, in her first full season on tour. At No. 32, the Canadian finished the season as the highest-ranked teenager.
590: Rankings spots jumped by 22-year-old Spaniard Pablo Carreno Busta, who began the season at No. 654 and is now No. 64, thanks to his domination of Futures tournaments.
5,214: Points separating No. 1 Williams and No. 2 Azarenka in the year-end WTA rankings. That is larger than the gap between Azarenka and No. 16 Ana Ivanovic.