Why is this a blunder?

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Avatar of Cairton

Here's a snippet of the end of a game I played recently. As you'll see, Toga II SE analyses Nxd7 as a blunder. Can't see why. If he takes my knight I've got mate, otherwise I win the exchange. Any thoughts?

Avatar of WindowsEnthusiast

After 17...Nf5! defending g7 and attacking your queen you lose a piece because he's taking the knight on d7 next. If you then try to fork his pieces with g4 then he pins that pawn with ...Qg6 and he keeps his extra material.

Avatar of Anatoly_Sergievsky

That should go on tactics trainer (for black) I would have missed that...

Avatar of Cairton

Ah! Thanks a lot Windows-7_. Much appreciated. I can stop scratching my head now.

Avatar of UnknownVision

Nf5!