Although their playing styles are different, Rafa and Rena have much in common. In fact, recently their careers have begun to mirror each other.
Their 2013 seasons look almost identical. Williams won 11 titles, two Grand Slams and went 78-4. Nadal won 10 titles, two Slams and went 75-7. Williams earned a record $12,385,572. Nadal earned $12,070,935.
Nadal rose from No. 4 to No. 1. His primary rival, Novak Djokovic, began the year No. 1 and won the Australian Open. Nadal missed the Aussie Open because of a knee injury.
Williams rose from No. 3 to No. 1. Her primary rival, Victoria Azarenka, began the year No. 1 and won the Australian Open. Williams injured her ankle in the fourth round and lost in the quarterfinals to Sloane Stephens.
Each has that killer instinct needed to put opponents away. They can never be counted out of matches.
Both were introduced to the game by family members. Williams' parents taught her to play. Nadal learned the game from his uncle, Toni Nadal.
They each suffered major injuries that took them away from the game. Williams missed a year after foot surgery and a subsequent pulmonary embolism. Nadal's chronic knee problems forced him to miss seven months.
They returned from these injuries to play better than ever.
Now, they are within striking distance of career achievements that once seemed impossible. Nadal needs just four more Grand Slam titles to match Roger Federer's 17. Williams needs one more to catch legends Martina Navratilova and Chris Evert. She needs six more to catch Steffi Graf. Graf's 22 are most in the open era.
The gap between Williams and the rest of the WTA is far greater than the margin between Nadal, Djokovic, Andy Murray and even Juan Martin del Potro.
Still, Williams and Nadal will begin 2014 as the favorites to maintain their No. 1 ranking and continue their record-setting paces.