|YouRang: K+2N vs. K+P is a notoriously difficult game to win. I suspect Lilienthal knew he wasn't going to win that way, so he hoped to set up a blunder trap (diagram after 81...Kd7 - white to move):
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Black is hoping for 82. b7??? Ne6#, but white didn't fall for it.
As <mjk> pointed out, black had a win. In fact, at move 75 he had mate-in-28 with 75...Kf6, but he played 75. Nf3? (mate-in-40), then gave up the win completely with 76...Nd5.
The winning technique in such a game is:
(1) Block the pawn with one knight.
(2) Use the other knight and king to force the opposing king into a corner. (The further advanced the pawn, the harder it is to find a corner and the right tempo that mates.) This is very difficult! The king and knight must do a very long and strange dance to work this out.
(3) At the right time (when the opposing king is sufficiently cornered), the knignt that was blocking the pawn approaches the cornered king with mating attack. This isn't quite as difficult as step 2, but it's riskier! If you time it wrong, the pawn may promote -- and then you lose!