Day 1 at the Australian Open

It's the opening day of what the tennis world calls the "Happy Slam" Down Under.

2013 Australian Open - Day 1

MELBOURNE, AUSTRALIA - JANUARY 14: Fernando Verdasco of Spain plays a backhand in his first round match against David Goffin of Belgium during day one of the 2013 Australian Open at Melbourne Park on January 14, 2013 in Melbourne, Australia. (Photo by Mark Kolbe/Getty Images)

2013 Australian Open - Day 1

MELBOURNE, AUSTRALIA - JANUARY 14: Samantha Stosur of Australia celebrates winning the first set in her first round match against Kai-Chen Chang of Chinese Taipei during day one of the 2013 Australian Open at Melbourne Park on January 14, 2013 in Melbourne, Australia. (Photo by Ryan Pierse/Getty Images)

Djokovic starts Australian Open defense

Serbia's Novak Djokovic, left, jokes with a member of his training staff during a training session at the Australian Open tennis championship in Melbourne, Australia, Sunday, Jan. 13, 2013. (AP Photo/Dita Alangkara)

Djokovic starts Australian Open defense

Switzerland's Roger Federer jokes with a cartoon character Sponge Bob Square Pants during an exhibition match during the Kids Tennis Day at Melbourne Park ahead of the Australian Open tennis championship in Melbourne, Australia, Saturday, Jan. 12, 2013. (AP Photo/Andy Wong)

Djokovic starts Australian Open defense

Serbia's Novak Djokovic and Serena Williams of the US perform the gangnam style dance during the Kids Tennis Day at Melbourne Park ahead of the Australian Open tennis championship in Melbourne, Australia, Saturday, Jan. 12, 2013. (AP Photo/Andy Wong)

Djokovic starts Australian Open defense

Britain's Andy Murray, right, listens to his coach Ivan Lendl during a practice session at Melbourne Park ahead of the Australian Open tennis championship in Melbourne, Australia, Saturday, Jan. 12, 2013. (AP Photo/Dita Alangkara)

Djokovic starts Australian Open defense

Russia's Maria Sharapova blows a kiss to the crowd following her win over compatriot Olga Puchkova in their first round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Jan. 14, 2013. (AP Photo/Andrew Brownbill)

Djokovic starts Australian Open defense

Russia's Maria Sharapova waves to the crowd following her win over compatriot Olga Puchkova in their first round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Jan. 14, 2013. (AP Photo/Andrew Brownbill)

Djokovic starts Australian Open defense

Serena Williams, centre, of the US celebrates with Serbia's Ana Ivanoic as Novak Djokovic looks on during an exhibition match on Rod Laver Arena during the Kids Tennis Day at Melbourne Park ahead of the Australian Open tennis championship in Melbourne, Australia, Saturday, Jan. 12, 2013. (AP Photo/Aaron Favila)