Umpire Alexandre Juge gave Kato a warning before Czech Marie Bouzkova and Spain's Sara Sorribes Tormo, on the other side of the net, asked for their opponents to be disqualified.
"No, no, let me explain to you. She (Kato) didn't do it on purpose, she (the ball girl) didn't get injured," Juge said.
"She didn't do it on purpose? She's crying," Sorribes Tormo said.
"And she has blood," Bouzkova added, prompting the umpire to go to see the ball girl, who was sobbing.
After speaking to the girl, the umpire went back up to his chair and announced the end of the match with the disqualification of Kato and Sutjiadi.
Bouzkova and Sorribes Tormo were leading 7-6 (1) 1-3 at the time.