Gold medallist Jones finished the race with a time of 24.27 seconds in front of silver medallist Pini who had a timing of 24.45s.
"It is great to come to Fiji and win in front of the enthusiastic crowd.
"The competition was very strong with the other swimmers also putting up a good show in the race.
"I will also be taking part in the 50 metres freestyle and 100 free style and butterfly in the competition as well. So I am looking forward to the event."
The 20-year-old from Brisbane is studying Economics Law from the University of Queensland. He said juggling through his studies and swimming was always hard for him.
"I think the people of Fiji motivated me to do well," he added.
"This morning while coming to the venue some local people wished me luck and I think it did wonders for me. It was also a great atmosphere which also contributed in the success.
"The people of Fiji are so friendly.
"Our stay has been very good so far with the accommodation and warm atmosphere."
Meanwhile, Daniel Hunter of New Zealand had to settle for the bronze medal while Fiji's Meli Malani finished sixth with a time of 25.35s.
Australian swimmer Cameron Jones after the medal ceremony at the Damodar City National Aquatic Centre last night.