Pavlyuchenkova defeated world number 85, Tamara Zidansek of Slovenia, 7-5, 6-3, with the unseeded Krejcikova fighting back from the brink to outlast Sakkari 7-5, 4-6, 9-7 after three hours and 18 minutes.
Browsing: Anastasia Pavlyuchenkova
But the early departure of seeded players in the women’s tournament continued as third-seeded Aryna Sabalenka was upset by Anastasia Pavlyuchenkova in the third round.
Also, world number three seed Naomi Osaka cruised past Russian Anastasia Pavlyuchenkova 6-1 6-2.
Muguruza is unseeded but has shown some of the form that brought her the French Open title in 2016 and Wimbledon a year later to put together her best run at Melbourne Park.
Unseeded Russian Anastasia Pavlyuchenkova ground down American fifth seed Sloane Stephens to reach the Australian Open quarter-finals.
Halep had to grind out a 7-6(9) 4-6 7-5 win over Russian Anastasia Pavlyuchenkova earlier in the day, completing a match that began Wednesday but was halted due to rain.
The Danish former world No 1, who joins Steffi Graf and Gabriela Sabatini with three Pan Pacific Open crowns, outclassed her Russian opponent 6-0 7-5 in 75 minutes to capture her first title of the year after losing in six previous finals.
Williams, the 13th seed, saw off 24th seed Pavlyuchenkova 6-4 7-6 (7-3) in the first fixture of the quarter-finals
Williams, the oldest player in the women’s singles, will now face Anastasia Pavlyuchenkova, who beat fellow Russian Svetlana Kuznetsova 6-3 6-3