19.Rf6! A brilliant move that sets up a mate threat on h7. If Black captures with 19… Bxf6, then after 20. e5, mate is inevitable on h7. The same happens if Black captures the knight on c3.
Benko played 19… Kg8, and after 20. e5! h6 21. Ne2!, he resigned because of 21… Nb5 22. Qf5, leading to mate, or 21… Bxf6 22. Qxh6, also leading to mate.
You are all set!
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