Lesson
White to move. Main line: 1. d4 Nf6 2. c4 g6 3. Nc3 Bg7 4. e4 d6 5. h3 O-O 6. Be3 c5 7. Nf3 Qa5 8. Nd2 cxd4 9. Nb3 Qxc3+ 10. bxc3 dxe3 11. f3 Nh5 12. Qc1 Bh6 13. g4 Nf4 14. Kd1 Ne6 15. Kc2 Nc6 16. h4 Bf4 17. Qd1 Ne5 18. Nc1 Bd7 19. a4 Rac8 20. Ne2 Bh6 21. g5 Bg7 22. Bh3 Nxf3 23. Qd3 Ne5 24. Qxe3 Nxc4 25. Qf2 Rc5 26. Rhb1 Bc6 27. Bg2 f5 28. gxf6 Bxf6 29. Rf1 Bxc3 30. Qxc5 Nxc5 31. Rxf8+ Kxf8 32. Kxc3 Ne5 33. a5 Nxe4+ 34. Bxe4 Bxe4 35. Nd4 Bd5 36. Nb5 a6 37. Nc7 Bc6 38. Rf1+ Kg7 39. Ne6+ Kh6 40. Rf8 Kh5 41. Rh8 h6 42. Rh7 Kxh4 43. Rxh6+ Kg4 44. Nd4 Kg5 45. Rh2 Bd5 46. Re2 Kf4 47. Rf2+ Nf3 48. Re2 e5 49. Nc2 Be4 50. Ne3 d5 51. Kb4 Nd4 52. Re1 Kf3
The sacrifice follows 8.Nd2 cxd4 9.Nb3. Instead of retreating the queen, Karthikeyan captures on c3 with check. After 10.bxc3 dxe3, White’s pawn structure is shattered and the king cannot castle.
Black develops with tempo, moves the king through d1 and c2, and keeps the knights and bishops active. The compensation is positional as well as material: weak dark squares, exposed king and coordinated minor pieces.
Queens eventually leave the board, but Black’s centralized king, bishop pair and passed pawns dominate the ending. The win takes 52 moves, which makes the sacrifice especially instructive: compensation can persist through simplification when it consists of structure, activity and king safety.