Raducanu, the reigning U.S. Open champion, failed on two chances to win the first set with Samsonova serving at 4-5. Raducanu subsequently went ahead 6-4 in the tiebreaker but lost the next four points.
Samsonova moved within one win of her second career WTA Tour final. She finished runner-up at the 2021 German Open.
Samsonova's semifinal foe will be China's Xiyu Wang (21), who upset fourth-seeded Victoria Azarenka (33) of Belarus 6-1, 6-3.
Sixth-seeded Kaia Kanepi (37) of Estonia came from behind to beat Russia's Anna Kalinskaya (23) 6-7 (4), 6-4, 6-3. Kanepi will next oppose Australia's Daria Saville (28), who defeated Canada's Rebecca Marino (31) 6-1, 7-5.
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Mubadala Silicon Valley Classic
Sixth-seeded Coco Gauff (18) couldn't build off her second-round win over Japan's Naomi Osaka (24), falling 7-6 (4), 6-2 to second-seeded Paula Badosa (24) of Spain in the quarterfinals at San Jose, Calif.
Badosa is through to her fourth semifinal of the year as she looks to capture her first tournament title since prevailing at Sydney, Australia, in mid-January.
Her semifinal opponent will be seventh-seeded Daria Kasatkina (25) of Russia, who rallied past fourth-seeded Aryna Sabalenka of Belarus 4-6, 7-5, 6-0.
On the other half of the bracket, Shelby Rogers (29) won an all-U.S. showdown against Amanda Anisimova (20), 6-4, 6-4. Rogers will face off in the semifinals against ninth-seeded Veronika Kudermetova (25) of Russia, who eliminated third-seeded Ons Jabeur (27) of Tunisia 7-6 (5), 6-2.
