On Sunday the 25-year-old came off the interchange bench to land a stunning 41m golden-point field goal to get the Dolphins home 34-32 over the Warriors and back into the NRL's top eight.
The disappointment of being dropped after playing round one in the No.7 jersey has only inspired O'Sullivan to try to get back a starting halves spot, if not this year then in 2025.
Kodi Nikorima and Isaiya Katoa are currently the Dolphins halves.
"I would love to play in the halves, but it is the cards I have been dealt at the moment, so I have just got to keep my head down and keep working hard," O'Sullivan told AAP.
"I am contracted for next year and I will still be a Dolphin. I will put my hand up to try and earn one of those halves spots. You never know in rugby league. All it takes is an opportunity."
O'Sullivan missed three months of action last year with a ruptured pectoral in a season where he was the first-choice half.
AAP has watched him studiously practise field goals after training for the past two years. Sunday's 83rd-minute effort was no fluke.
"It is just not an overnight thing. Every day you are practising. It's great that it finally gets to pay off," O'Sullivan said.
"It's funny. (Centre) Jake Averillo was passing me the ball at captain's run training and I swear I missed all five shots at field goal. I said, 'it's all right, I won't need that', but I ended up needing it, which was pretty cool.
"So long as Wayne (Bennett) is happy. I love playing for him and he is very honest with me. I am happy I could make him proud.
"It has been an up-and-down year, so it was unreal to put some icing on the cake. I am just grateful to be part of this great club and this great team."O'Sullivan's father is recruitment guru Peter O'Sullivan, who put the Dolphins roster together with aplomb in a short space of time. Peter has taken the head-of-recruitment position at Newcastle, but Sean said he was not going to follow him.
"No way in the world. I am happy here at this great club. We have a family up here and I bought my first house here too," he said.
"It is tough (to bid farewell to Peter), but I am also very proud of him. He got an unreal offer to go there and is the best in the business. I know Newcastle are going to fix their stuff, and he is the right man for that."
Despite a lean two months, O'Sullivan said he had no doubt the Dolphins could play finals and make an impact."Why can't we? We have to fix a few things, obviously our defence. We leak way too many points, but we are working really hard on that," he said.
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