Two Puzzles from the US Championships

When is a human player better than a computer? Every so often a position arises in which a top-class human player can see the solution more quickly than a machine. The first of the two puzzles that follow (both taken from the same game) is just such a position. I watched the game between Nemcova and Virkud live on Chess.com, listening to the commentary while keeping an eye on another chess website where viewers were kibitzing, relying largely on their chess engines. There was universal surprise, therefore, when Nemcova played what is in fact the best move in the position, but one that the machines did not list among their first three or four options. The live grandmaster commentators did, however, see the move and didn't consider any others worth discussing. Can you find the solution? The key is not just to see the line by guessing or by a process of elimination, but to understand the concept behind it. White has a completely dominant position, but is it time to try to convert the advantage into material, is it best to manoeuver, or how should white make progress?

Well done if you found the right move, but the real kudos goes to those who found the idea behind it.

The second problem arose immediately after this in the same game, but this time you must play black's position. Virkud faced a problem that all chess players are too familiar with - how to choose the best of several evils. White's position in the game is close to winning, but Nemcova was under mild time pressure and the process of converting the win was not immediately straightforward. How can you complicate white's task?