Wildcard entrant Birrell booked herself a spot in the last 16 after a dazzling display against the world No.9 in front of a boisterous home crowd at Pat Rafter Arena.
The Queensland local will either face top-30 players Dayana Yastremska or Anastasia Potapova, who play later on Wednesday.
"I've spent so many hours on this court since I was little," Birrell said.
"I watched the Brisbane International when I was a kid and to get here to have a tournament that's basically at home is so special.
"I get to play in front of my family and friends and it's not very often that my player's box is completely full.
"I'm so, so happy and thank you so much to everyone (in the crowd) for supporting me."
Birrell, world No.113, defied rankings in the two-hour-and-three-minute affair and claimed the first break point on her way to winning the opening set.
She then broke US Open semi-finalist Navarro to begin the second.
Bringing the heat in Brisbane 🥵🥵🥵— wta (@WTA) @kimbirrell98 | #BrisbaneTennis pic.twitter.com/UbreHymJsKJanuary 1, 2025
The American looked to have flicked a switch after claiming consecutive games to go up 4-2, but Birrell remained relentless.
So close was the second set arm-wrestle that Birrell was broken three times and Navarro four.
Powered on by the crowd, the 26-year-old set up match point with her first ace before Navarro sent the ball in the net to hand over the victory.
Fellow Australian wildcard Maya Joint takes on former world No.1 Victoria Azarenka later on Wednesday.
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