Five reasons why Serena Williams is the world's No. 1

Updated 1750 GMT (0150 HKT) May 20, 2015
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In recent years, Serena Williams has been the undisputed force in women's tennis. The American has won an incredible 19 grand slam titles and is looking to triumph at the French Open for a third time. But what is it that sets Serena apart from her rivals?
Ahead of this year's French Open in Paris, CNN sat down with Patrick Mouratoglou -- who began coaching Williams in 2012. Their trophy tally since teaming up includes a Wimbledon title, an Olympic gold medal, three U.S. Open titles, a Roland Garros title and an Australian crown, lifting her back up to the pinnacle of the women's game
Mouratoglou outlines the five main reasons for her dominance of the game.
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"First reason, I would say, is the ability to win, which means she refuses to lose," says Mouratoglou of the star who first turned pro 20 years ago. "She's an unbelievable competitor." Williams' first grand slam title came at the 1999 U.S. Open, where she defeated Martina Hingis in the final. Matthew Stockman/Getty Images/File
"Second, I think she's probably the most professional player on tour," explains Mouratoglou. "Her focus, her dedication ... she's unbelievably professional." The 33-year-old has won 66 WTA titles during her career.
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"Three, of course, her power. She's the most powerful player by far," says Mouratoglou. "She hurts opponents with her strokes, forehand, backhand, serve, whatever. So that's the third reason." Roslan Rahman/AFP/Getty
"The fourth is that she aims high all the time, and when she doesn't do unbelievably well she considers it unprofessional -- that's her word for it. If she's making more than three double-faults in a match she says it's unacceptable, so she's very demanding with herself." FREDERIC J. BROWN/AFP/Getty Images
"The fifth? Her serve is, for me, the best in women's tour of all time, and if I have to give one example the first tournament we won together was Wimbledon 2012. During that tournament she served more aces than any women or men. And men play five sets. Completely incredible." PATRICK KOVARIK/AFP/Getty Images