The fifth seed, a finalist at the U.S. Open last year, won eight of the last 11 games in a topsy-turvy contest on Margaret Court Arena to secure a last-16 meeting with the final Australian in the draw, Daria Gavrilova.
"I was a little bit lucky today, I think she was probably the best one but I am very happy to be in the fourth round for the first time," said the 24-year-old Czech.
"When she was 5-2 she was missing a little bit more, I was just staying in the game, even if I broke my racket. I was just trying to get every ball in as she was playing so fast and aggressive."
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Ostapenko's first attempt to serve for the match ended with a double fault and a grin from the Latvian but the second ended in tears after she slapped a straightforward backhand into the net.
The fired up world number 38, who mixed 41 winners with 43 unforced errors over the contest, saved one match point at 5-6 in the decider but looked to have run out of steam as the match drew to its conclusion.
Pliskova had needed just an hour to get through each of her first two matches at Melbourne Park but needed a shade over two hours to see off the 19-year-old, who conceded victory when she clattered a backhand into the net post.
(Reporting by Nick Mulvenney, editing by Pritha Sarkar)
