Answer
The answer is eight. In 1933, Helen Jacobs defeated Betty Nuthall in the semifinals of the U.S. National Championships. Nuthall was ranked fourth among American female players at the time. There were eight American male players ranked higher than Nuthall, including Wilmer Allison, Sidney Wood, Frank Shields, Ellsworth Vines, George Lott, Berkeley Bell, Gregory Mangin, and Clifford Sutter.