context: 1. g1f3  1... d7d5  2. e2e3  2... g8f6  3. c2c4  3... e7e6  4. b1c3  4... c7c6  5. b2b3  5... b8d7  6. c1b2  6... f8d6  7. d2d4  7... e8g8  8. f1e2  8... b7b6  9. e1g1  9... c8b7  10. d1c2  10... f8e8 In these positions from the Semi-Slav Defense there's always a question about how to develop the heavy pieces, since several configurations are possible, especially for the rooks. The most common development is with the queen on e7 and the rooks on c8 and d8, supporting a possible c6-c5. 11. a1d1  11... d8c7 The queen takes an alternative route. 12. h2h3  12... a7a6 Preparing c6-c5 without White having Nb5. Another plan is Rad8-Qb8. 13. f1e1 This doesn't seem like the scariest of moves, but the problem for White in this line is that the e3-e4 advance isn't that promising and patience is needed. 13... c6c5 A new and natural move. 14. c4d5  14... e6d5  15. d4c5  15... b6c5 Hanging pawns on the board. This typical pawn structure is probably the second most important in chess, after the isolated queen's pawn. 16. f3h4 White prepares an active plan. This is a bit risky, but has good practical value for a blitz game. 16... d7e5  17. h4f5  17... d6f8  18. f2f4 A bold decision. 18... e5d7  19. e2f3  19... g7g6 The losing mistake. Black has two acceptable alternatives. 20. c3d5 This isn't a sacrifice, just a tactical operation that wins a pawn. 20... f6d5  21. f3d5  21... b7d5  22. d1d5  22... c7c6  23. c2c3  23... f7f6  24. e1d1  24... g6f5  25. d5d7 White is a pawn up and has the better structure and attacking chances. 25... e8e6  26. e3e4 Opening the path for the queen. 26... a8e8  27. c3g3  27... g8h8  28. e4f5  28... e6e3  29. d7h7 A nice finishing touch. 29... h8h7  30. g3g6  30... h7h8  31. b2f6  31... c6f6  32. g6f6  32... f8g7  33. f6h4  33... h8g8  34. f5f6  34... g7h8  35. h4g5  35... g8f7  36. d1d7 