RIO DE JANEIRO, BRAZIL - AUGUST 07: Novak Djokovic of Serbia shows his emotion as he waves to the crowd after his defeat against Juan Martin Del Potro of Argentina in their singles match on Day 2 of the Rio 2016 Olympic Games at the Olympic Tennis Centre on August 7, 2016 in Rio de Janeiro, Brazil. (Photo by Clive Brunskill/Getty Images) (2016 Getty Images)
Juan Martin del Potro, of Argentina, raises his arms after defeating Novak Djokovic, of Serbia, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Novak Djokovic, of Serbia, returns to Juan Martin del Potro, of Argentina, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, returns to Novak Djokovic, of Serbia, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, returns to Novak Djokovic, of Serbia, in the men's tennis competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Vadim Ghirda) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, right, is embraced by Novak Djokovic, of Serbia, after del Potro won in two tie break sets at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Novak Djokovic, of Serbia, returns to Juan Martin del Potro, of Argentina, in the men's tennis competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Vadim Ghirda) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Novak Djokovic, of Serbia, reaches down as he carefully tries to direct a moth away during his match against Juan Martin del Potro, of Argentina, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, cries after defeating Novak Djokovic, of Serbia, in the men's tennis competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Vadim Ghirda) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Novak Djokovic, of Serbia, compliments Juan Martin del Potro, of Argentina, on his return at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Novak Djokovic, of Serbia, returns to Juan Martin del Potro, of Argentina, in the men's tennis competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Vadim Ghirda) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, raises his arms after defeating Novak Djokovic, of Serbia, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, reacts after losing a point to Novak Djokovic, of Serbia, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, cries after defeating Novak Djokovic, of Serbia, in the men's tennis competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Vadim Ghirda) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
A pickup truck lays destroyed next to a house damaged by a mudslide in Xaltepec, on the mountainous north of Puebla state, Mexico, Sunday, Aug. 7, 2016. The death toll from the remnants of Hurricane Earl grows to more than 30 in Mexico as a new tropical storm forms off the country's Pacific Coast. (AP Photo/Pablo Spencer) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, right, is embraced by Novak Djokovic, of Serbia, after del Potro won in two tie break sets at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Fans cheer for Novak Djokovic, of Serbia, during his match against Juan Martin del Potro, of Argentina, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Charles Krupa) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)
Juan Martin del Potro, of Argentina, reacts after winning a point against Novak Djokovic, of Serbia, in the men's tennis competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016. (AP Photo/Vadim Ghirda) (Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistribu)