Spain's Rafael Nadal celebrates after defeating United States' Frances Tiafoe in their quarterfinal match at the Australian Open tennis championships in Melbourne, Australia, Tuesday, Jan. 22, 2019. [Photo: AP]"

Spain's Rafael Nadal, top, waits for a return shot from United States' Frances Tiafoe during their quarterfinal match at the Australian Open tennis championships in Melbourne, Australia, Tuesday, Jan. 22, 2019. [Photo: AP]"

Spain's Rafael Nadal serves to United States' Frances Tiafoe during their quarterfinal match at the Australian Open tennis championships in Melbourne, Australia, Tuesday, Jan. 22, 2019. [Photo: AP]"