The U.S. champion received a score of 66.73 to edge Russian star Irina Slutskaya by .03 of a point. Japanese skaters Shizuka Arakawa and Fumie Suguri were third and fourth while Kimmie Meissner of the United States was fifth.
Emily Hughes, who joined the American team after Michelle Kwan decided she was not healthy enough to compete, was seventh. Hughes is the sister of 2002 Olympic champion Sarah Hughes.
Twenty-nine skaters were entered in the women's event and Cohen was the last one to compete in the short program. She did not take the ice until 11:15 p.m. local time, but the late-night performance turned out to be worth waiting for.
Meissner, on the other hand, was the second to perform -- more than four hours before Cohen.
The long program that will determine the medals will be skated Thursday night.