Cameron van der Burgh represented South Africa at the 2012 Olympics.
Van der Burgh led the qualifiers into Wednesday's final with a time of 26.81 seconds. Zorzi managed 27.44, keeping out Brazilian Felipe Lima, who won bronze in the 100m breaststroke.
The 25-year-old Van der Burgh was happy that two South African swimmers advanced to the final. "I'm very happy for Giulio who is swimming at his first world championships and I wish him well," Van der Burgh said.
"I'll pass on my experiences to help him pull through for tomorrow. Tomorrow anything can happen from any lane."
Van der Burgh, who won the silver medal in the 100m breaststroke on Monday, said he was better equipped for the 50m breaststroke event.
"Sometimes you focus too much on the world record or a gold medal and then it doesn't happen. I'll just focus on what I can control which is the swim. The 50m is better suited to the skills I have and the training I have done."
Zorzi, who would be swimming in his first final at a major championship, said he was happy with his performance.
"I felt really good in the warm-up and had a great start, but in the race there were one or two things that didn't go well and I'll correct them for tomorrow," he said. – Sapa