PARIS — Amanda Anisimova smacked one last backhand winner to complete her upset of defending champion Simona Halep in the French Open quarterfinals, flung her racket and covered her mouth with both hands.Eyes wide, Anisimova then spread her arms with palms up and said, “What?!”In a tournament filled with surprises, Anisimova provided the latest Thursday. Just 17 and ranked merely 51st, yet possessing the mindset and mien of someone much more experienced and accomplished, the American withstood a late charge by Halep and won 6-2, 6-4 to reach her first Grand Slam semifinal.”I don’t think it will sink in, at least not for today. Yeah, I mean, it’s crazy,” said Anisimova, who was born in New Jersey to Russian parents and moved to Florida when she was 3. “I really can’t believe the result today. And getting the opportunity to play against Simona, that’s amazing. But how it ended is even crazier to me.”That’s a fair assessment of the entire tournament. Serena Williams, No. 1 Naomi Osaka and No. 2 Karolina Pliskova lost in the third round; Angelique Kerber and Caroline Wozniacki were gone in the first.The highest-seeded player in the semifinals is No. 8 Ash Barty, the Australian who…