Osaka's Qatar title bid ended by Pliskova after Swiatek downs Azarenka
Four-time Grand Slam title winner Osaka, who is rebuilding her career after maternity leave, went down 7-6 (8/6), 7-6 (7/5).
It was the 26-year-old Japanese star's second defeat to Pliskova this year after losing in three sets in her comeback tournament in Brisbane last month.
Pliskova, ranked at 59, will face world number one Iga Swiatek for a place in Saturday's final.
The Czech's win over Osaka, clinched in one hour and 43 minutes, was her ninth in the last 10 days, a run which included the Transylvania Open title on Sunday.
Defending champion Swiatek moved closer to a third successive Qatar title when she brushed aside Victoria Azarenka 6-4, 6-0 in 74 minutes in her quarter-final.
Polish 22-year-old Swiatek is 12-1 at the Gulf tournament with her only defeat coming in the 2020 second round to Svetlana Kuznetsova.
Former world number one Azarenka, the 2012 and 2013 champion in Doha, double-faulted in the ninth game to hand Swiatek the first break.
The top seed served it out before racing through the second set without facing a break point.
Swiatek ended the encounter with 17 winners to just five from Azarenka.
Earlier, Elena Rybakina and Anastasia Pavlyuchenkova set-up a semi-final clash.
Third seed and former Wimbledon champion Rybakina came from 4-2 down in the first set to defeat 2021 US Open finalist Leylah Fernandez 6-4, 6-2.
Pavlyuchenkova secured her first 1000-level hardcourt semi-final in 14 years with a 7-5, 6-4 win over Danielle Collins of the United States.
"I hope it will be a good match, we know each other well, both on and off the court," said Rybakina, last weekend's champion in Abu Dhabi, of her clash with Pavlyuchenkova.
Pavlyuchenkova, ranked 32 in the world, needed one hour and 34 minutes to see off Collins, a former world number seven who had to qualify this week.
The Russian's only stutter came in the first set when she coughed up a 5-2 lead but she regrouped to take it 7-5 and went on to claim victory on her first match point.
"I was injured for a long time, so I'm happy to be back and able to fight on all points, and victories give me confidence," said Pavlyuchenkova in the post-match on-court interview.
"I've been working a lot on the mental aspect and I feel like it's paying off," added the 32-year-old, a finalist at the French Open in 2021.
