The match went to three sets, with Williams taking the first set then dropping the second two for a final score of 2-6, 6-4, 6-4.
Vinci advanced to the semifinals after beating 40th-ranked Kristina Mladenovic in the quarters. She will now face Flavia Pennetta for the title.
Vinci is currently ranked 43rd in the world and is a five-time Grand Slam champion in women’s doubles. She also has a career Grand Slam in doubles, which only five women’s pairs have achieved. Vinci had faced Serena four times previously and had never beaten her — and had never even taken a set off her, according to ESPN.