US OPEN '18: On the clock! 25-second countdown's Slam debut

Any discussion of the serve clocks that will make their Grand Slam debut during the U.S. Open's main draw starting Monday, and could become a regular part of tennis as soon as next year, inevitably turns to Rafael Nadal and Novak Djokovic.

They are two of the greatest players in history — and two of the slowest between points. For one thing, Djokovic's incessant bouncing of the ball before a service toss delays things. So do Nadal's habitual mannerisms: the touching of the nose, the tucking of the hair, the grabbing at the shorts, and on it goes.