Serena Williams targets Evert & Navratilova's Grand Slam mark

Serena Williams tells BBC Radio 5 live that overtaking the 18 Grand Slam singles titles won by Chris Evert and Martina Navratilova is a "big incentive" for her.

The 31-year-old American, who beat Maria Sharapova in three sets in the Miami final on Saturday, currently has 15 to her name and says their mark of 18 is "in her sights". Australian Margaret Court holds the record with 24.

Williams describes herself as a "maniac" who is always looking to improve and says she has not thought about how long she will continue in the sport.