The Czech second seed has now won her last five matches over qualifier Mladenovic in straight sets.
The Czech star beat Estonia's Anett Kontaveit 6-3, 7-6 (7/2) in the final, succeeding compatriot Karolina Pliskova as champion at the clay-court event.
Kvitova sustained damage to the tendons in her hand, along with injuries to all five fingers and two nerves, and underwent nearly four hours of surgery.
The 33-year-old Radim Zondra, who is currently in prison for another crime, was sentenced on charges of serious battery and illegal entry into Kvitova's flat.
Second-seeded Petra Kvitova is now the highest-ranked player remaining in the tournament after Osaka's shock elimination.
Having played only two Grand Slam quarter-finals since her Wimbledon triumph in 2014, Kvitova joked last year that she might as well quit playing at the top four events.
With Kvitova on the team, the Czechs have won six of the last eight Fed Cups.
Osaka held three match points at 5-3 in the second set but couldn't close it out. She allowed Kvitova to come back and win 23 of 27 points to take that set and go up 1-0 in the third.
The 25-year-old American was every bit Petra Kvitova's equal during their Australian Open semifinal during the time Rod Laver Arena's retractable roof was open.
Osaka is bidding to become the first woman since Serena Williams in 2015 to win the US and Australian Opens back to back.
Collins, who had a dream run to make the final four on her Australian debut, became flustered after Kvitova won a first-set tie-breaker and her game fell apart in the second set.
Petra Kvitova overtook Halep after going through to the Australian Open semi-final.
The two-time Wimbledon champion will now face unseeded American Danielle Collins in the semi-final.
The diminutive Barty, 22, has been in sizzling form, winning seven of eight matches this year to back up a title victory in Zhuhai late last year.
The Czech eighth seed struggled with her serve early in the match before finding her rhythm for a 6-3, 6-2 victory.