Career
Her best Grand Slam singles tournament was when she reached the 1970 French Open final, losing to Margaret Court 6–2, 6–4. Masthoff was the runner-up at that tournament in 1971, losing to Billie Jean King 6–3, 6–2. Masthoff teamed with Kathleen Harter to reach the women"s doubles final at the 1976 French Open, losing to the team of Fiorella Bonicelli and Gail Sherriff Lovera 6–4, 1–6, 6–3.
According to Bud Collins, Masthoff was ranked in the world top ten in 1970, 1971, and 1973, reaching a career high of World Number.
6 in 1970.
Singles (1 runner-up)
Doubles (1 runner-up)
A = did not participate in the tournament.