A King's Knight's Gambit at the odds of the Queen's Knight. Morphy presses on the king's side, and after a Rook sacrifice on the 25th move Black resigns rather than submit to the exchange of his remaining pieces and the loss of a Pawn.
20…Re8Black should have retaken the Pawn with the Kt.
22…d5Black could not escape without some loss, but 22. B. to B's sq. would have been the correct play, as that would only have involved the sacrifice of the exchange.
25.Rxh6This sacrifice forces the game.
28.Qxf4+Black resigned at this point, foreseeing that his adversary could compel the exchange of the two remaining pieces, and win by means of his extra Pawn.
J. Löwenthal, Morphy's Games of Chess (1860) · Public domain · source