Djokovic's tears weren't for the pain — after he fell and twisted his right ankle in the third game against Sam Querrey — but for being able to finish the match and not let down his teammates.
The 25-year-old Djokovic — even with the swollen ankle — ran off the last nine games in a row and completely dominated Querrey, 7-5 6-7 6-1 6-0, to give his team a 3-1 win and a spot in the semi-finals against Canada.
The courageous Serb said he probably would have quit playing if the match was in a regular tournament but fought through the pain because it was a team event.
"If I had not been playing for Serbia with my team beside me, I am not sure I would have carried on," Djokovic said.
"It couldn't have happened at a worse moment, right at the start of the match," he added. "I felt pain with every motion in the first 30 minutes so I just had to go for precision with my shots."
Djokovic required treatment on the court but carried on with his hobbled ankle to the cheers of his teammates as motivation.
"I am very emotional about the win today," he said. "It meant a lot to me personally. It meant a lot to the whole team."
You have to admire this guy's fortitude and loyalty. It's no surprise he's No. 1 in the world.