Embarrasment of Power

I came across this endgame exercise, I don't know who maded it up but I think it's pretty cool and sweet. Underpromotion is defined as "Promoting a pawn when it reaches the eight rank to less than a Queen." This is a little used tactical resource. There are times, infrequent to be sure, when, for some reason or other, the more powerful Queen will not do. Underpromotion is, indeed, a rarity. The position below is one of those unique situations where too much power is a handicap. White to play and win...