Germany's Philipp Kohlschreiber reacts after beating John Isner of the US during their 2012 US Open men's third round singles match at the USTA Billie Jean King National Tennis Center in New York on September 3, 2012. AFP PHOTO/Emmanuel Dunand (Photo credit should read EMMANUEL DUNAND/AFP/GettyImages)
TEN-US OPEN-ALMAGRO
Nicolas Almagro of Spain shouts at his corner during his match against Tomas Berdych of the Czech Republic during their men's singles match at the 2012 US Open tennis tournament September 3, 2012 in New York. AFP PHOTO/DON EMMERT (Photo credit should read DON EMMERT/AFP/GettyImages)
TEN-US OPEN-IVANOVIC-PIRONKOVA
Ana Ivanovic of Serbia reacts after winning against Tsvetana Pironkova of Bulgaria during their 2012 US Open women's singles match at the USTA Billie Jean King National Tennis Center in New York on September 3, 2012. AFP PHOTO / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/GettyImages)
TEN-US OPEN-IVANOVIC-PIRONKOVA
Ana Ivanovic of Serbia returns against Tsvetana Pironkova of Bulgaria during their 2012 US Open women's singles match at the USTA Billie Jean King National Tennis Center in New York on September 3, 2012. AFP PHOTO / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/GettyImages)
2012 US Open - Day 8
NEW YORK, NY - SEPTEMBER 03: Tomas Berdych of Czech Republic returns a shot during his men's singles fourth round match against Nicolas Almagro of Spain on Day Eight of the 2012 US Open at USTA Billie Jean King National Tennis Center on September 3, 2012 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Cameron Spencer/Getty Images)
2012 US Open - Day 8
Nicolas Almagro of Spain looks on during his match against Tomas Berdych of the Czech Republic during their men's singles match at the 2012 US Open tennis tournament September 3, 2012 in New York. AFP PHOTO/DON EMMERT (Photo credit should read DON EMMERT/AFP/GettyImages)
TEN-US OPEN-WILLIAMS-HLAVACKOVA
(Photo credit TIMOTHY A. CLARY/AFP/GettyImages)
TEN-US OPEN-WILLIAMS-HLAVACKOVA
Serena Williams of the US reacts after winning against Andrea Hlavackova of the Czech Republic during their 2012 US Open women's singles match at the USTA Billie Jean King National Tennis Center in New York on September 3, 2012. AFP PHOTO / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/GettyImages)
TEN-US OPEN-WILLIAMS-HLAVACKOVA
Serena Williams of the US returns against Andrea Hlavackova of the Czech Republic during their 2012 US Open women's singles match at the USTA Billie Jean King National Tennis Center in New York on September 3, 2012. AFP PHOTO / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/GettyImages)
TEN-US OPEN-WILLIAMS-HLAVACKOVA
Andrea Hlavackova of the Czech Republic returns against Serena Williams of the US during their 2012 US Open women's singles match at the USTA Billie Jean King National Tennis Center in New York on September 3, 2012. AFP PHOTO / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/GettyImages)
2012 US Open - Day 8
NEW YORK, NY - SEPTEMBER 03: Angelique Kerber of Germany celebrates a point against against Sara Errani of Italy during their women's singles fourth round match Day Eight of the 2012 US Open at USTA Billie Jean King National Tennis Center on September 3, 2012 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Cameron Spencer/Getty Images)
2012 US Open - Day 8
NEW YORK, NY - SEPTEMBER 03: Anett Kontaveit of Estonia plays against Madrie Le Roux of South Africa during their junior girls' singles first round match on Day Eight of the 2012 US Open at USTA Billie Jean King National Tennis Center on September 3, 2012 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Matthew Stockman/Getty Images)
2012 US Open - Day 8
NEW YORK, NY - SEPTEMBER 03: Sara Errani of Italy returns a shot against Angelique Kerber of Germany during their women's singles fourth round match Day Eight of the 2012 US Open at USTA Billie Jean King National Tennis Center on September 3, 2012 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Cameron Spencer/Getty Images)
2012 US Open - Day 8
NEW YORK, NY - SEPTEMBER 03: Mike Bryan (L) and Bob Bryan of the United States tap hands during their men's doubles third round match against Santiago Gonzalez of Mexico and Scott Lipsky of the United States on Day Eight of the 2012 US Open at USTA Billie Jean King National Tennis Center on September 3, 2012 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Matthew Stockman/Getty Images)
2012 US Open - Day 8
NEW YORK, NY - SEPTEMBER 03: Angelique Kerber of Germany returns a shot against Sara Errani of Italy during their women's singles fourth round match Day Eight of the 2012 US Open at USTA Billie Jean King National Tennis Center on September 3, 2012 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Cameron Spencer/Getty Images)