The unseeded Croat, a former teenage prodigy whose career was derailed by personal trauma, used all her experience to upset the Czech 6-4, 3-6, 6-4 in a Rod Laver Arena epic, before collapsing on court in tears.
Her emotional win sets up a last-four clash with either six-time champion Serena Williams or British hope Johanna Konta for a place in the final to write another chapter in her inspiring story of perseverance.
Venus Williams plays fellow American Coco Vandeweghe in the other semi-final.
"To me, this is overwhelming. I will never forget this day and the last couple of weeks. This has truly made my life, and everything bad that happened, (it) has made it okay."
Her comeback has been the feel-good story of the tournament, having dropped out of top-level tennis for most of the 2003-2010 period after fleeing an abusive father and suffering money and injury problems.
It makes her the only Croatian woman to get so far at a major since her exploits at Wimbledon 18 years ago.
But it was a bitter pill to swallow for Pliskova, who was aiming to match her US Open exploits last year when she made the final, beating Serena Williams en route.
- Apply pressure -
==================
Ranked 79, Lucic-Baroni beat third seed Agnieszka Radwanska on her way to the quarter-finals as she rides a wave of popular support.
The Czech began to apply pressure and scored an early break to go 2-1 in front when Lucic-Baroni sprayed a forehand wide.
But her advantage didn't last with the plucky Croat starting to read the booming Pliskova serve, nailing her returns and breaking back to level at 3-3.
Lucic-Baroni was playing aggressive tennis with Pliskova struggling to counter attack, and she deservedly took the set in 32 minutes when the fifth seed sent a forehand long.
A medical timeout for what appeared to be blisters on her right foot seemed to unsettle Lucic-Baroni, with Pliskova returning to hold serve then break again to take control, sealing the second set comfortably.
They traded breaks in a nervous third set until Lucic-Baroni finally held to take a 3-1 advantage. It didn't last long in a seesawing match with Pliskova clawing back to 3-3.
But after Lucic-Baroni went off for a medical timeout for treatment to her left leg, she returned to hold serve and break again, and then served out the match.
Disclaimer: No Business Standard Journalist was involved in creation of this content
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