Switzerland's Roger Federer reacts after a point against Spain's Rafael Nadal during the men's singles final of the Australian Open tennis tournament on Sunday.

Serena Williams of the US celebrates her victory against Venus Williams of the US during the women's singles final on day 13 of the Australian Open tennis tournament in Melbourne on January 28, 2017. (AFP Photo)

Serena Williams of the US (R) holds the trophy at the awards ceremony following her victory over Venus Williams of the US (L) in the women's singles final on day 13 of the Australian Open tennis tournament in Melbourne on January 28, 2017. (AFP Photo)