Her second round match with Suzanne Lenglen at the 1921 U.S. National Championships brought Mallory her greatest celebrity. Before the match, Bill Tilden advised Mallory to "hit the cover off the ball." Once the match began, Mallory "attacked with a vengeance" and was ahead 2–0 (40–0) when Lenglen began to cough. Mallory won the first set 6–2 and was up 40–0 on Lenglen's serve in the first game of the second set when Lenglen began to weep and walked to the umpire's stand and informed the official that she was ill and could not continue. After the match, the USTA accused Lenglen of feigning illness. The French Tennis Federation (FTF) exonerated Lenglen and accepted her testimony (and a doctor's) that she had been ill. However, Albert de Joannis, vice president of the FTF who accompanied Lenglen during her trip to the United States, quit his post in protest of the FTF's conclusion. He claimed that Lenglen was "perfectly fit" during the match and that, "She was defeated by a player who on that date showed a better brand of tennis."