- Roger Federer tumbles in year-end rankings
- Andy Murray, Angelique Kerber new year-end No. 1s
- Maria Sharapova drops out of rankings
(CNN)Roger Federer, Maria Sharapova, Andy Murray and Angelique Kerber -- among others -- all played their part in a tennis season of firsts. It won't soon be forgotten -- or duplicated, and here's why...