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US tennis great Billie Jean King poses before the start the match between Serena Williams of the US and Caroline Wozniacki (R) of Denmark during their 2014 US Open Women's Singles - finals match at the USTA Billie Jean King National Tennis Center September7, 2014 in New York. TIMOTHY A. CLARY/AFP/Getty Images ( 533133323 )

Serena Williams of the United States serves to Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454874398 )

Caroline Wozniacki of Denmark serves to Serena Williams of the United States during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images) ( 454870124 )

Serena Williams of the United States returns a shot against Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Julian Finney/Getty Images) ( 454869976 )

Nick Jonas performs the National Anthem as a giant American flag is displayed on court prior to the women's singles final on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454867948 )

Nick Jonas performs the National Anthem prior to the women's singles final on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Julian Finney/Getty Images) ( 454870554 )

Serena Williams of the US hits a return to Caroline Wozniacki of Denmark during their US Open 2014 women's singles finals match at the USTA Billie Jean King National Center September 7, 2014 in New York. STAN HONDA/AFP/Getty Images ( 533135355 )

Caroline Wozniacki, of Denmark, serves against Serena Williams during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Darron Cummings) ( 2014 US Open Tennis )

Serena Williams, returns a shot against Caroline Wozniacki, of Denmark, during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Darron Cummings) ( 2014 US Open Tennis )

Caroline Wozniacki of Denmark serves to Serena Williams of the US during their US Open 2014 women's singles finals match at the USTA Billie Jean King National Center September 7, 2014 in New York. STAN HONDA/AFP/Getty Images ( 533135465 )

Serena Williams of the US serves to Caroline Wozniacki of Denmark during their US Open 2014 women's singles finals match at the USTA Billie Jean King National Center September 7, 2014 in New York. STAN HONDA/AFP/Getty Images ( 533135390 )

Caroline Wozniacki of Denmark serves to Serena Williams of the US during their 2014 US Open Women's Singles - finals match at the USTA Billie Jean King National Tennis Center September 7, 2014 in New York. TIMOTHY A. CLARY/AFP/Getty Images ( 533136299 )

Mother Oracene Price watches as Serena Williams of the United States plays against Caroline Wozniacki of Denmark on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Julian Finney/Getty Images) ( 454871312 )

Serena Williams serves against Caroline Wozniacki, of Denmark, during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Charles Krupa) ( 2014 US Open Tennis )

Caroline Wozniacki of Denmark returns a shot against Serena Williams of the United States during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Julian Finney/Getty Images) ( 454869382 )

Serena Williams of the US plays against Caroline Wozniacki of Denmark during their 2014 US Open Women's Singles - finals match at the USTA Billie Jean King National Tennis Center September 7, 2014 in New York. TIMOTHY A. CLARY/AFP/Getty Images ( 533135571 )

Serena Williams of the US hits a return to Caroline Wozniacki of Denmark during their US Open 2014 women's singles finals match at the USTA Billie Jean King National Center September 7, 2014 in New York. STAN HONDA/AFP/Getty Images ( 533135493 )

Caroline Wozniacki, of Denmark, returns a shot against Serena Williams during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Darron Cummings) ( 2014 US Open Tennis )

Serena Williams of the United States serves to Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454872364 )

Caroline Wozniacki, of Denmark, serves against Serena Williams during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Julio Cortez) ( 2014 US Open Tennis )

Serena Williams of the United States returns a shot against Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Julian Finney/Getty Images) ( 454872392 )

Caroline Wozniacki of Denmark hits a return to Serena Williams of the US during their US Open 2014 women's singles finals match at the USTA Billie Jean King National Center September 7, 2014 in New York. STAN HONDA/AFP/Getty Images ( 533135502 )

Serena Williams of the United States returns a shot against Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Al Bello/Getty Images) ( 454873504 )

Caroline Wozniacki of Denmark returns a shot against Serena Williams of the United States during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454872110 )

Serena Williams of the United States reacts against Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454872346 )

Serena Williams of the United States serves to Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454869890 )

Caroline Wozniacki of Denmark returns a shot against Serena Williams of the United States during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Matthew Stockman/Getty Images) ( 454872096 )

Serena Williams serves against Caroline Wozniacki, of Denmark, during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Julio Cortez) ( 2014 US Open Tennis )

Caroline Wozniacki, of Denmark, returns a shot against Serena Williams during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Mike Groll) ( 2014 US Open Tennis )

Caroline Wozniacki of Denmark looks on against Serena Williams of the United States during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Julian Finney/Getty Images) ( 454873730 )

Serena Williams of the US prepares to serve to Caroline Wozniacki of Denmark during their US Open 2014 women's singles finals match at the USTA Billie Jean King National Center September 7, 2014 in New York. STAN HONDA/AFP/Getty Images ( 533135383 )

Caroline Wozniacki of Denmark returns a shot against Serena Williams of the United States during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454869680 )

Serena Williams of the United States returns a shot against Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Streeter Lecka/Getty Images) ( 454871156 )

Caroline Wozniacki, of Denmark, reaches for a shot against Serena Williams during the championship match of the 2014 U.S. Open tennis tournament, Sunday, Sept. 7, 2014, in New York. (AP Photo/Charles Krupa) ( 2014 US Open Tennis )

Serena Williams of the United States reacts against Caroline Wozniacki of Denmark during their women's singles final match on Day fourteen of the 2014 US Open at the USTA Billie Jean King National Tennis Center on September 7, 2014 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Julian Finney/Getty Images) ( 454872362 )

Caroline Wozniacki of Denmark takes her break between games during match against Serena Williams of the US at the 2014 US Open Women's Singles - finals match at the USTA Billie Jean King National Tennis Center September 7, 2014 in New York. TIMOTHY A. CLARY/AFP/Getty Images ( 533136104 )