The Day They Belabored the Point

[snopes]

Twenty-five years ago, on Sept. 24, 1984, Vicki Nelson and Jean Hepner, who were ranked No. 93 and No. 172 in the world, engaged in a 29-minute, 643-shot rally that remains the longest point played in a professional tennis match.

http://www.nytimes.com/2009/09/23/sp.../24tennis.html