This is the third time she has won the honour after claiming it in 2002 and 2008.
There was more joy for Serena as she and sister Venus were named 2009's top doubles team.
Belgian Kim Clijsters, who won the 2009 US Open title, received the Comeback Player of the Year award and also won her seventh Karen Krantzcke sportsmanship award from the WTA.
Another Belgian who won recognition was Yanina Wickmayer. Wickmayer, who reached the US Open semi-finals and won two WTA titles in 2009, won the Most Improved Player award.
American Melanie Oudin picked up the Newcomer of the Year Award, and the Player Service Award was won by Liezel Huber for the fourth time.
Sania disappoints in Auckland
Sania down eight places to 92nd in rankings
Serena Williams retains her Australian Open title
Jankovic survives marathon, Clijsters exits
Sania battles her way into last eight