Serena Williams, at 15 years old, stretches for a forehand return during her first round match against Italian Laura Golarsa at the Sydney International Tennis Tournament in 1998. She went on to win the match 6-3 6-1 in her first match on Australian soil.
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Venus (l.) and sister Serena Williams laugh as they celebrate their doubles win at the 1999 US Open. The Williams sisters defeated Sandrine Testud of France and Chandra Rubin of the United States 4-6, 6-1, 6-4 to win the title.
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Serena Williams holds her trophy after winning the 1999 Gaz de France Open in Paris. Williams won her first title on the WTA Tour that year, beating Amelie Mauresmo 6-2, 3-6, 7-6, (7-4) in the final of the $520,000 Gaz de France Open.
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Serena Williams poses with photos of her four consecutive grand slam victories in early 2003 on the banks of the Yarra River in Melbourne, Australia. The world number one completed her sweep of the four tournaments that make up the grand slam when she at last added the Australian Open to the French, Wimbledon, and US Open championships she won in 2002.
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At the 2005 Australian Open in Melbourne, Serena Williams, seeded seventh, chases a shot from Russia's Nadia Petrova, the number 11 seed. Williams defeated Petrova 6-1, 3-6, 6-3.
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Serena Williams returns the ball to her opponent Ashley Harkleroad, of the US, at the 2008 French Open at Roland Garros stadium in Paris.
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Serena Williams (r.) greets her sister Venus at the net after defeating her in their quarter-final match at the 2008 US Open at Flushing Meadows in New York.
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Serena Williams holds her trophy after defeating Venus Williams in their ladies' singles finals match at the 2009 Wimbledon tennis championships in London.
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Serena Williams (l.) talks with tournament referee Brian Earley (2nd r.) and an official as a line judge (r.) stands by during her match against Kim Clijsters of Belgium at the 2009 US Open in New York. Clijsters won the match 6-4, 7-5, which ended in controversy when Williams was called for a foot fault on a second serve to go match point down.
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Serena (l.) and Venus return to Czech Republic's Andrea Hlavackova and Lucie Hradecka in the women's doubles tennis gold medal match at the All-England Lawn Tennis Club during the London 2012 Olympic Games.
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Serena Williams (r.) embraces her father and coach Richard Williams as her sister Venus looks on, after defeating Agnieszka Radwanska of Poland to win the women's singles final match at the 2012 Wimbledon Championships.
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Serena Williams (l.) and her sister Venus laugh together on the podium after receiving their gold medals in women's doubles at the All-England Lawn Tennis Club in Wimbledon, London at the 2012 Summer Olympics.
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Serena Williams celebrates defeating Maria Sharapova of Russia in their women's singles final match at the 2013 French Open at Roland Garros stadium in Paris. World number one Williams clinched her second French Open title when she beat defending champion Sharapova 6-4, 6-4 in the final.
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Serena Williams reacts after winning a point against opponent Sloane Stephens at the 2013 US Open in New York.
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Serena Williams celebrates her victory against Li Na of China after their WTA tennis championships final match in Istanbul in 2013.
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Serena Williams hits a return to Daniela Hantuchova of Slovakia during their women's singles match at the 2014 Australian Open in Melbourne.
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Serena Williams walks off the court with a broken racquet during her WTA Championships singles semi-final tennis match against Caroline Wozniacki of Denmark at the Singapore Indoor Stadium in 2014.
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Serena Williams hits a return to Maria Sharapova of Russia during their women's singles final match at the Australian Open in Melbourne in Jan. 2015.
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Serena Williams poses with her trophy and her dog, Chip, in the dressing room after winning the women's singles final match against Lucie Safarova of the Czech Republic during the French Open at Roland Garros stadium in Paris, in June 2015.
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Serena Williams reacts after winning the second set of her match against Victoria Azarenka of Belarus at the Wimbledon Championships in London, in July 2015.