Let us call the rank 1 player, Player 1, and the rank 2 player, Player 2. There are 8 starting positions in the tournament tree. Let Player 1 occupy a random spot within this 8. Three of the remaining spots will lead to Player 2 losing to Player 1 before the final. The other four will lead to Player 2 losing to Player 1 in the final. The simplest way to see this is to draw out the tournament tree. $$ $$ Therefore, the probability of Player 2 losing to Player 1 in the final is $$ P = \frac{4}{7} $$