France's Monfils, ranked 19th in the world, pulled out shortly before his scheduled quarter-final against Thiem with left Achilles tendon trouble.
"I wouldn't believe I win today again", Bencic said.
Andreescu will play the victor of the second semifinal between No. 23 seed Belinda Bencic of Switzerland and No. 8 seed Angelique Kerber of Germany in Sunday's final. "I'm definitely playing how I feel it, and it's going well so I'm not planning on changing that".
Women: Belinda Bencic bt Karolina Pliskova 6-3, 4-6, 6-3; Angelique Kerber bt Venus Williams 7-6 (3), 6-3. "I'm not going to the court with any expectation".
Mari Osaka, a year-older than her 21-year-old sister who has shot to the top of the rankings thanks to back-to-back Grand Slam titles at the USA and Australian Opens, has twice played in WTA doubles made draws, most recently with Naomi at the 2017 Toray Pan Pacific Open.
"Venus is just such a great player and an incredible champion", Kerber said about her opponent, who came on to the court with a heavily taped right knee.
Serbian teenager Kecmanovic failed to convert any of his three break-point opportunities against a ruthless Raonic, who unleashed a torrent of punishing groundstrokes on a sunny and breezy day. From the get-go, Kerber made strong in-roads into Williams' serve, especially the second serve and was just as relentless on her own serves.
Canada's Bianca Andreescu will meet sixth seed Elina Svitolina of Ukraine in the other Indian Wells semi-final. She's here as a wildcard, and she beat a lot of good players. She was coming off a straight-set upset of defending champion and top-ranked Naomi Osaka in the fourth round.
"When you're confident, you can really just trust your instincts and you don't have to think about it at all", Bencic said.
Federer, the 20-time Grand Slam champion who claimed his 100th career title at Dubai last month, takes on 67th ranked Hubert Hurkacz of Poland while Nadal faces 12th-seeded Russian Karen Khachanov.
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