Caroline Wozniacki is the No. 1 woman in tennis, a sport that requires steely nerves, ruthless tactics and a willingness to antagonize opponents until they have a meltdown.

Her nickname? Sunshine.

On Monday night, Wozniacki hustled her way to a 6-7(6), 7-5, 6-1 comeback win that put her in the U.S. Open quarterfinals, one round from a potential...