London • Novak Djokovic and Serena Williams are the International Tennis Federation's world champions for 2013.
Djokovic captured the men's award for the third straight year, and Williams took the honor for the fourth time.
Djokovic started the year by winning a third straight Australian Open and was runner-up at Wimbledon and the U.S. Open. The 26-year-old Serb finished the season No. 2 in the ATP rankings with seven tour titles.