Ashton Ward's hamstring injury looks to have cleared the way for Sullivan to start in the halves next to Cody Walker against fellow finals hopefuls Canterbury on Friday.
Ward pulled up sore while kicking a conversion in Saturday's tense defeat of Parramatta, and fellow halves option Jamie Humphreys is contending with a minor foot injury that may rule him out.
This year, Sullivan has felt the impact of the NRL's new interchange rule, which allows teams to name six players on their bench but still only select four to play during a game.
On six occasions, Sullivan has suited up for game day, only to go unused by coach Wayne Bennett.
On three of those occasions, scheduling meant Sullivan was unable to play reserve grade, so did not get the chance to play footy at all on those weekends.
It has left Sullivan to float between either earning extended minutes in reserve grade, or playing bit parts or not at all at NRL level.
"Unfortunately, it's a s*** position to be in, because I still want to be in that first-grade team, whether that's being on the bench," Sullivan said.
"(But) I haven't really been a big fan of the six-man bench.Â
"It's frustrating because I've been healthy all year and haven't really been playing much footy."
But as reward for his patience, Sullivan looks set for extended time starting in the halves, and maybe even a maiden NRL finals appearance.
Since making his first-grade debut in 2020, the 24-year-old has played 60 first-grade games across stints with St George Illawarra, Wests Tigers and Souths.
But no team Sullivan has played on has reached the top eight in that time.
Sullivan's last brush with sudden-death footy was the SG Ball Cup grand final in 2019, when he captained Illawarra to victory over a Manly side featuring Josh Schuster, Ben Trbojevic and Kaeo Weekes.
"(NRL finals) would be an amazing opportunity, especially to do it at South Sydney and with this playing group," Sullivan said.
"I'm going to take it as it comes, I've still got to be in that team."
It is a bittersweet feeling for Sullivan that his first finals chance could come at the expense of good mate and fellow Wollongong product Ward.
"I'm sending my love to him, he's been outstanding this year," Sullivan said.
"Seeing him get hurt, especially doing his hammy, I've done a few hammy as well. It's a pretty s*** feeling."
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