Possessing surrendered the opening established for a few matches in a row, Sabalenka took a one-established guide for the very first time in Melbourne but was unable to build on it as her serving problems resurfaced once all over again.
Kanepi was gifted a double break early in the next set with again-to-back double faults from her 23-12 months-previous opponent and did not squander the possibility as she cruised to a 4- lead right before taking the established.
The 36-year-outdated carried that momentum into the decider and seemed set to go 5-3 up but Sabalenka saved four crack factors to maintain for 3-4 and stage it, before suffering a service meltdown once more and hitting 3 double faults in four details.
Kanepi was manufactured to work for her victory immediately after staying not able to near the match from 40- up as Sabalenka saved four matchpoints, but the Estonian prevailed in the tiebreak and converted her fifth matchpoint to total the upset.
Kanepi will take on Polish seventh seed Iga Swiatek, who conquer Sorana Cirstea 5-7 6-3 6-3 previously on Monday, for a place in the past 4.