LONDON — Trailing 5-4 in her first Wimbledon quarterfinal, Sloane Stephens already had saved two set points and was about to serve at deuce when a fairly nondescript match became anything but. Raindrops were falling and Stephens' opponent, 2007 runner-up Marion Bartoli, was trying to persuade a tournament official the Court 1 grass was dangerously slick. Spectators were booing and derisively whistling, angry at the prospect of play being suspended.