Djokovic, the No. 1 seed in the tournament, was trailing Pablo Carreño Busta, 6-5, in the first set of a fourth-round match.
The 15-time major winner carded a 1-under-par 70 in the opening round as he uncharacteristically struggled with his iron game.
The 15-time major winner will play alongside Jordan Spieth and England's Justin Rose in the first two rounds.
Williams was handed three code violations and called umpire Carlos Ramos "a thief."
What other sporting events are on during the World Cup?
The European tour is considering Trump's course for 2019.
The U.S. Tennis Association has to decide if it will give the disgraced tennis star wild card entry.
The Briton has endured "the toughest stretch of my career."
The American 14-time major tournament winner will be out the game for six months.
The sportswear giant has sponsored the Russian for over a decade.
The two men arguably are the greatest rivalry in tennis.
The two Italians faced off after upsetting the No. 1 and No. 2 seeds.
The tennis star was the No. 1 seed in the women's semifinals.
Serena Williams will face off against Roberta Vinci of Italy at 11 a.m. ET on Friday.
On Tuesday evening, Serena defeated Venus and Djokovic prevailed against Lopez to advance.
The quarterfinals begin without Andy Murray, who exited the tournament in an upset Monday.
As the tournament enters its second week, temperatures remain high and the stakes get higher.
A record number of players have already had to retire from the tournament.