Just 24 hours after posting a stunning 7-5 7-5 win over world No.8 Emma Navarro, the wildcard took down world No.35 Potapova in 106 minutes in front of adoring fans at Pat Rafter Arena.
Birrell's career was on thin ice when an elbow injury cost her almost three years on tour.
It was during that time out that the world No.113 worked as part of the media team at the Brisbane International.
But Birrell was the star attraction on Thursday, holding her nerve against a player ranked 78 places higher to secure a WTA event last-eight appearance for the first time.
After the match, Birrell welled up as she recounted her tough journey back to full fitness.
"It's been a long road," she said.
"I have had a few injuries, but as does everyone who plays professional sport - everyone has their trials and tribulations in life.
"I've been super lucky to have such an incredible family and team behind me.
"They believed in me when I didn't even think I was going to get back on court.
"They encouraged me. They're pretty much the only reason why I'm back playing at this level today."
Kimberly Birrell joins her mother Ros after another emotional win in Brisbane. (Jono Searle/AAP PHOTOS)
Birrell will take on either world No.55 Anhelina Kalinina or world No.49 Yue Yuan in the quarters.
"I'm totally speechless," Birrell added.
"I really believe in the way I'm playing, and anything can happen. Especially playing at home."
Birrell was broken in her first service game against Potapova, but she quickly broke back and dominated the rest of the opening set without quite capitalising on a glut of golden opportunities.
The 26-year-old Gold Coast talent had break point chances in the fifth, seventh, ninth and 11th games, but wasn't able to convert any of those eight opportunities.
Unforced errors proved Birrell's undoing for most of those chances, while three stunning winners from Potapova in the 11th game saved three break points on that occasion.
It was a different story in the tiebreak as Birrell produced a clinical display to race out to a 4-0 lead on the way to sealing the first set in 66 minutes.
Brissy Birrell 🔥— Brisbane International (@BrisbaneTennis) A super high level from both players in the opening set with @kimbirrell98 taking it out in a tiebreak.#BrisbaneTennis pic.twitter.com/nK4H9dRHgBJanuary 2, 2025
Potapova's building error count proved costly in the second set as Birrell snared the early break and then broke again to cruise to victory.
"She's a quality player and credit to her, she played so well in the big points," Birrell said.
"I just kept telling myself to keep going. I was creating opportunities.
"I thought eventually I was going to get there. When I got to the tiebreaker, I felt like I had been on top the entire set, so I felt quietly confident.
"And then when I got the break in the second set, it felt so good. I'm super happy."
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