The second set was a back and forth arm wrestle as both refused to take a backwards step.
Another tiebreaker unfolded with Pavlyuchenkova getting the upper hand and moving on where she'll take on 17th seed Angelique Kerber.
Pavlyuchenkova's dominance was clear and the numbers after the contest showed how stark it was, with Pavlyuchenkova hitting 43 groundstroke winners compared to Pliskova's 19.
Pavlyuchenkova had never beaten Pliskova in their six previous meetings, but held her nerve in the tense second set tiebreak to secure the 7-6 7-6 victory after a two hours and 25 minute battle.
Pliskova was also previously unbeaten in 2020, having won the season-opening Brisbane International and then two more matches in Melbourne.
Then, just a few minutes later, Bencic fell to Anett Kontaveit in a 6-0 6-1 mauling that lasted just 49 minutes.
The latest upsets makes it nine out of the top 16 women's seeds being eliminated.
The carnage includes three of the four favourites with bookmakers after Serena Williams and Naomi Osaka were bundled out on Friday.
Only Aussie Ash Barty is still standing.