U.S. Open Pressure Points: No. 1 seed Serena Williams and her race against time

Approaching 35 and with a new challenger to her throne, can the all-time great do it again?
Read more: http://www.tennis.com/pro-game/2016/08/serena-williams-2016-us-open-angelique-kerber-steffi-graf-22-grand-slam-titles/60188/?source=Snapzu