Late Wednesday night, as the Washington Nationals reached their most perilous moment in weeks, a foul ball rolled to Jayson Werth in the on-deck circle at Citizens Bank Park. In his former home, a place that welcomes old heroes back with raging jeers, Werth injected one more slice of drama into a night that lacked none. The out-of-town scoreboard had delivered bad news. The Philadelphia Phillies' go-ahead run, hours after the Nationals had taken a commanding lead, had died on the warning track. The Nationals' firm control of the National League East, six months in the making, had begun to teeter.