Four trained shelter dogs that once roamed the streets of Sao Paulo found themselves center stage at the Brazil Open tournament.

In an exhibition match with players Roberto Carballes Baena of Spain and Gastao Elias of Portugal, the canines Frida, Costela, Mel and Isabelle engaged onlookers by picking up balls that went out of bounds.

The shelter dogs, wearing orange ribbons and trained for months, spent almost a half-hour tracking down balls often intentionally missed by the 122nd and 140th ranked players. Baena and Elias will play for real Friday in the ATP tournament's quarter-finals.

A dog picks up a tennis ball during the Brazil Open tournament in Sao Paulo, Brazil

Tennis player Roberto Carballes of Spain walks with a couple of dogs during an exhibition game

At the command of their trainer Andrea Beckert, the dogs retrieved the balls with their teeth and ran off the court to their trainer. The unusual initiative was made to promote the adoption of abandoned street animals.

Beckert said the biggest difficulty was to make the animals more confident and playful. 'These are dogs that were mistreated. 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,' she told journalists. The basic commands that the dogs learned were 'pick the ball,' ''let it go,' ''stay' and 'come.'

The organizer of the ball-dog initiative, Marli Scaramella, said that all four still live in shelters. 'The idea is to show people that a well-fed and well-treated animal can be very happy. We have more than 1,000 dogs in our care,' she said.

Tennis players Gastao Elias, left, from Portugal and Roberto Carballes from Spain enter the tennis court with four trained ball retrieving dogs, during an exhibition match

Four trained shelter dogs that once roamed the streets of Sao Paulo found themselves center stage at the ATP 250 Brazil Open tournament

Portugal's Gastao Elias receives a ball from a dog during the Brazil Open tennis tournament in Sao Paulo