Michael Gordon added the extras to open up a 6-0 lead, but the outstanding Greg Bird, another former Shark, helped level the scores when he bulldozed his way over the line after 25 minutes before Kelly raced away with 90-metre interception for four points.
Titans five-eighth Aidan Sezer missed the kick, giving the visitors a 10-6 lead at halftime.
The second half saw the Sharks control the early passages of play and they regained the lead when Wade Graham's effort - disallowed by the on-field officials - was overruled by the video referee and Gordon kicked the goal.
A Sezer penalty put the Titans back on level terms before fullback Zillman got the final touch to Kelly's kick to give his side a winning start to the new campaign.
Titans prop Luke Douglas set a new record with his 195th successive NRL match.
Gallen said he was confident of a return to action within three to four weeks and believes the problem isn't as bad as a similar injury he picked up earlier in his career.
"It's a terrible start to the year, I could feel it. It just got stuck. It's one of those things," Gallen said.
"I hard something crack, so I knew I did something straight away.
"I did it in a trial game in the 2006-07 season, so I knew what it was. They said then I'd miss six weeks but I only missed three to four games. I don't think it's as bad as that."
Titans coach John Cartwright was delighted with his side's efforts and said he thought the result should have been more comprehensive with an Albert Kelly try ruled out in the second half with the video referee ruling he lost control of the ball.
"I can't see how they come up with the decision they did," he said.
"I saw no separation, just the ball coming down on the line. But you get some good ones and get some bad ones."
- AAP
