Guido Pella of Argentina hits a return during the men's singles quarterfinal match against Rafael Nadal of Spain at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Guido Pella of Argentina hits a return during the men's singles quarterfinal match against Rafael Nadal of Spain at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Rafael Nadal of Spain hits a return during the men's singles quarterfinal match against Guido Pella of Argentina at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Guido Pella of Argentina hits a return during the men's singles quarterfinal match against Rafael Nadal of Spain at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Rafael Nadal of Spain hits a return during the men's singles quarterfinal match against Guido Pella of Argentina at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Lorenzo Sonego of Italy hits a return during the men's singles quarterfinal match against Dusan Lajovic of Serbia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Dusan Lajovic won 2-0. (Xinhua/Nicolas Marie)

Rafael Nadal of Spain hits a return during the men's singles quarterfinal match against Guido Pella of Argentina at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Lorenzo Sonego of Italy hits a return during the men's singles quarterfinal match against Dusan Lajovic of Serbia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Dusan Lajovic won 2-0. (Xinhua/Nicolas Marie)

Rafael Nadal of Spain hits a return during the men's singles quarterfinal match against Guido Pella of Argentina at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Rafael Nadal of Spain hits a return during the men's singles quarterfinal match against Guido Pella of Argentina at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Guido Pella of Argentina hits a return during the men's singles quarterfinal match against Rafael Nadal of Spain at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Rafael Nadal of Spain hits a return during the men's singles quarterfinal match against Guido Pella of Argentina at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Nadal won 2-0. (Xinhua/Nicolas Marie)

Dusan Lajovic of Serbia hits a return during the men's singles quarterfinal match against Lorenzo Sonego of Italy at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Dusan Lajovic won 2-0. (Xinhua/Nicolas Marie)

Novak Djokovic of Serbia hits a return during the men's singles quarterfinal match against Daniil Medvedev of Russia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Novak Djokovic of Serbia hits a return during the men's singles quarterfinal match against Daniil Medvedev of Russia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Dusan Lajovic of Serbia hits a return during the men's singles quarterfinal match against Lorenzo Sonego of Italy at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Dusan Lajovic won 2-0. (Xinhua/Nicolas Marie)

Daniil Medvedev of Russia hits a return during the men's singles quarterfinal match against Novak Djokovic of Serbia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Dusan Lajovic of Serbia hits a return during the men's singles quarterfinal match against Lorenzo Sonego of Italy at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Dusan Lajovic won 2-0. (Xinhua/Nicolas Marie)

Daniil Medvedev of Russia hits a return during the men's singles quarterfinal match against Novak Djokovic of Serbia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Daniil Medvedev of Russia hits a return during the men's singles quarterfinal match against Novak Djokovic of Serbia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Daniil Medvedev of Russia hits a return during the men's singles quarterfinal match against Novak Djokovic of Serbia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Novak Djokovic of Serbia hits a return during the men's singles quarterfinal match against Daniil Medvedev of Russia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Novak Djokovic of Serbia hits a return during the men's singles quarterfinal match against Daniil Medvedev of Russia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Novak Djokovic of Serbia hits a return during the men's singles quarterfinal match against Daniil Medvedev of Russia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Daniil Medvedev of Russia hits a return during the men's singles quarterfinal match against Novak Djokovic of Serbia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Borna Coric of Croacia hits a return during the men's singles quarterfinal match against Fabio Fognini of Italy at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Novak Djokovic of Serbia hits a return during the men's singles quarterfinal match against Daniil Medvedev of Russia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Daniil Medvedev won 2-1. (Xinhua/Nicolas Marie)

Fabio Fognini of Italy hits a return during the men's singles quarterfinal match against Borna Coric of Croacia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Fabio Fognini of Italy hits a return during the men's singles quarterfinal match against Borna Coric of Croacia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Borna Coric of Croacia hits a return during the men's singles quarterfinal match against Fabio Fognini of Italy at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Borna Coric of Croacia hits a return during the men's singles quarterfinal match against Fabio Fognini of Italy at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Fabio Fognini of Italy hits a return during the men's singles quarterfinal match against Borna Coric of Croacia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Borna Coric of Croacia hits a return during the men's singles quarterfinal match against Fabio Fognini of Italy at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Fabio Fognini of Italy hits a return during the men's singles quarterfinal match against Borna Coric of Croacia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Fabio Fognini of Italy hits a return during the men's singles quarterfinal match against Borna Coric of Croacia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)

Fabio Fognini of Italy hits a return during the men's singles quarterfinal match against Borna Coric of Croacia at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, April 19, 2019. Fabio Fognini won 2-1. (Xinhua/Nicolas Marie)