Frances Tiafoe of the United States serves during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Hu Jingchen)

Rafael Nadal of Spain hits a return during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Bai Xuefei)

Rafael Nadal (R) of Spain shakes hands with Frances Tiafoe of the United States during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Hu Jingchen)

Rafael Nadal of Spain reacts during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Bai Xuefei)

Rafael Nadal of Spain celebrates after the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Bai Xuefei)

Rafael Nadal of Spain reacts during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Hu Jingchen)

Rafael Nadal of Spain hits a return during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Hu Jingchen)

Rafael Nadal of Spain competes during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Bai Xuefei)

Rafael Nadal of Spain gestures after the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Bai Xuefei)

Rafael Nadal of Spain reacts during the men's singles Quarterfinals match between Rafael Nadal of Spain and Frances Tiafoe of the United States at the 2019 Australian Open in Melbourne, Australia, on Jan. 22, 2019. Rafael Nadal won 3-0. (Xinhua/Hu Jingchen)