En Prise Primer - can't see a quick mate

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En Prise Primer - Obstruction of Opponent's Pieces

In this chess mentor exercise Bobby Fisher is going for a quick mate on Benko:  white Rf6  ...Bxf6 

It works if ... Bxf6 , but what happens if ...Kg8 instead of Bxf6 ???.

I  really can't see a quick mate then.   Do I overlook something here ? Has someone, with  access  to this particular chess mentor exercises , an idea ?

 

 

 

Possies

Forgot to give you the link, here it is:

http://www.chess.com/chessmentor/view_lesson?id=7208