All eyes will be on Kelleher when she runs out for her first international game in Australia's Women's Rugby League World Cup opener on Friday against Samoa.
It will be another milestone for the 26-year-old after she played a starring role in the Sydney Roosters NRLW premiership push and made her first start in the halves for NSW in the Women's State of Origin earlier this year.
But Kelleher has a huge weight of expectation on her after coach Jess Skinner made "one of the hardest phone calls of (her) life" to leave mainstay five-eighth Ali Brigginshaw out of the World Cup squad.
Headlines have swirled about the decision, but Sergis is confident the Roosters star will not only continue her lethal partnership with halfback Tarryn Aiken but also flourish in the occasion.
"I'm just really excited to see her finally get her opportunity here in the squad. She's been up there for such a long time and being in the squad last year, she never got her opportunity," Sergis said.
"She's just had such a big year, the likes of Origin at the start and then obviously building us into that premiership, only a few weeks ago.
"Her confidence has skyrocketed, and she's really found her role, really found her voice, and she's really backing herself."
The Jillaroos will be ones to beat this World Cup as they are on a rampaging run of form which has included thumping both the world No.2 New Zealand and No.3 England last year.
They also boast nine players in the NRLW's Dally M team of the year, but Sergis insists the side isn't feeling any pressure to live up to their hype.
She also expects that Friday's clash at CommBank Stadium won't be a walk in the park.
"With Samoa, we're so excited. They're such a big pack, so we're really looking forward to that physicality," Sergis said.
"I know it's going to be a battle, and they've got some really big bodies that are going to really test us."
For Sergis, the game will also mean a lot to her, as it will be her 15th in the green and gold.
"2017 (Australia's last home World Cup) was my chance to debut and obviously did my knee that year, so I never got that opportunity," the centre said.
"It could potentially be the last one we have here, so it would just be the best feeling in the world (to win)."
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