Catherine Cartan "CiCi" Bellis is an American former professional tennis player. In early 2018, she was the second youngest player in the top 100 of the WTA rankings. Bellis has a career-high ranking of world No. 35 by the Women's Tennis Association, which she achieved in August 2017. She is known for winning a match at the 2014 US Open as a 15 year old against a top-20 opponent, making her the youngest match-winner at the US Open since 1996.