Brazil Open's highlight on Thursday was not the tennis players, but rather four formerly abandoned dogs that have been taught to be "Tennis Ball Dogs," where they fetch out-of-bound balls and bring them back to the players.

The event serves an exhibition to promote the practice of adopting abandoned street animals. The dogs, which were rescued from Sao Paulo, wore orange bandanas while showcasing their fetching talents during a game between Roberto Carballes Baena of Spain and Gastao Elias of Portugal, according to TIME.

The dogs - Costela, Frida, Isabelle and Mel - heeded the command of their trainer, Andrea Beckert, all throughout the exhibition.

"We want to show that abandoned dogs can be adopted and trained. After all, it's not easy to get a dog to only pick up the lost balls, and then to give them up," said Beckert, a trainer from the Association of Animal Wellbeing, CNN reported.

Beckert shared the difficulties of training the dogs, saying that it was more difficult than regular dogs because these were abused canines. "...We have to make them adapt, feel the environment, the court, the noise of the balls and the noise of the people. Some are doing well, others are still a little scared,'' Beckert said, according to Associated Press.

The commands that the dogs are now familiar with are "pick the ball," "let it go," "come" and "stay."