A rook for a knight, on purpose
Round four, move 17. His knight came to h5 and I took it with the rook, which is a rook for a knight and the engine puts me a pawn and a half worse straight afterwards. It is still the engine's second move of the 36 legal ones there, so it is not a blunder, it is a price.
I paid it because his defence had to be exact and mine did not. That turned out to be measurable: on his next move the engine gives him exactly one move out of 35 that keeps him better, and he played a different one. He had the same one-move choice three more times before the end and found it once.
The move the engine actually wanted was 17.Ne4, and its line is my game move for move with the rook still on h1. So the position I bought was on the board for free. I would still play it against him.