Who has won the most season-ending championships in ATP tennis?

1. Most ATP
World Tour Finals Titles
(Singles version)

2. What are the World Tour Finals?
 The ATP World Tour Finals (the actual name has
undergone several changes the past 4 decades) is the
annual, season-ending tournament, usually held in
November, comprising of the top eight singles and
doubles players.
 Unlike the other tournaments, the players are split to two
groups of four, and they play three round robin matches
to determine the winners of the group who will then
advance to the knock-out stages.

3. Ilie Nastase
 1971 vs. Stan Smith
 1972 vs. Stan Smith
 1973 vs. Tom Okker
 1975 vs. Bjorn Borg

4. Ivan Lendl
 1981vs. Vitas Gerulaitis
 1982 vs. John McEnroe
 1985 vs. Boris Becker
 1986 vs. Boris Becker
 1987 vs. Mats Wilander

5. Pete Sampras
 1991 vs. Jim Courier
 1994 vs. Boris Becker
 1996 vs. Boris Becker
 1997 vs. Yevgeny Kafelnikov
 1999 vs. Andre Agassi

6. Roger Federer
 2003 vs. Andre Agassi
 2004 vs. Lleyton Hewitt
 2006 vs. James Blake
 2007 vs. David Ferrer
 2010 vs. Rafa Nadal
 2011 vs. Jo-Wilfried Tsonga

7. Image Sources
 http://www.lta.org.uk/News/British-tennis-weekly-features/World-tennis-
news/2011/November/World-Tennis-News-round-up---28th-November/
 http://bigstory.ap.org/content/ivan-lendl
 http://www.ciaobucarest.it/Ilie%20Nastase.html
 http://tennis-pronostics.com/tournament/barclays-atp-world-tour-finals