Nagelsen won in 1978 and 1980, the competition in the women's doubles at the Australian Open. The first victory she celebrated with Renáta Tomanová against Naoko Sato and Pam Whytcross, the second with Martina Navratilova against Ann Kiyomura and Candy Reynolds. In 1978, she also reached the final in Melbourne, but it lost to Chris O'Neil in two sets. In its 21 years lasting career on the WTA Tour Nagelsen won three singles and 24 doubles titles. After her retirement from the professional tour in 1996, she worked as a commentator for ABC News and ESPN in the United States and for Nine Network in Australia.
Betsy Nagelsen married the sports manager Mark McCormack, founder of International Management Group (IMG ) and member of the International Tennis Hall of Fame. Donations help the couple the McCormack - Nagelsen Tennis Center was established at the College of William & Mary.