interesting that Courier chose Harrison to play the dbls.
seldom does the composition of the double given on thursday really mean anything about what it will be on saturday.
Very often the captains do as Courier did : for the draw nominate two players for singles and the two other ones for doubles but on saturday they can decide whichever composition they want.
I know Harrison has a good serve-and-volley but I believe more in Fish or Isner playing the double, except maybe if they play a long match on friday : Isner already played with one of the Bryan brothers (don't remember which one
) in Serbia in 2010 and they won.
By the way, in Serbia that year, Isner also took Djokovic to 5 very tight sets on indoor clay (and he had already played two matches before, one in 4 and one in 5 sets). He played very well that day.
Fed says that the tie will be tight, and I understand that he's careful.