Victoria Azarenka of Belarus, the former world number one, was defeated by Swiatek in just 74 minutes, 6-4 6-0.
In the semi-finals, the Pole—who has won her last 11 matches in Doha—will take on Karolina Pliskova, who is playing well.
Czech Pliskova won 7-6 (8-6) 7-6 (7-5) to stop Osaka’s best run in over two years.
The four-time major champion Osaka, who gave birth to her daughter Shai in July, started playing tennis again last month.
She had not advanced this far in a competition since losing to Swiatek in the Miami Open final in April 2022, when she faced Pliskova in the quarterfinals.
At the Transylvania Open on Sunday, Pliskova—who won her first WTA victory in four years—was broken by Osaka in her opening service game, but she quickly responded to win the opening set tie-break.
In the second set, Osaka forced a tiebreaker by saving two match points at 5-4 and 6-5, but Pliskova wrapped up the victory at the fourth attempt after an hour and forty-three minutes.
In contrast, 2022 Wimbledon champion Elena Rybakina secured her place in the last four by rallying from a 4-1 deficit in the opening set to defeat Canadian Leylah Fernandez 6-4 6-2 in the Doha women’s tournament.
The Russian Anastasia Pavlyuchenkova, who overcame Danielle Collins, will square up against the third-seeded Kazakh.
