The Trompovsky Attack

1 d4 Nf6 2 Bg5

I am surprised to learn that this is the third-most popular move here for white.

2...c5

This is black's best move, based on success rates in the 365chess database. White has weakened his dark squares on the queen-side with his second move, and 2...c5 immediately takes action against those dark squares.

3 Bxf6

Played about half the time, this is what black has to get used to, the idea that he allows his king-side pawns to be messed up right off the bat. But he has compensation! Besides 3 Bxf6, the other main move is 3 d5. A sample game is Bouaziz-Labib(2000), which continued 3...Qb6 4. Nc3 Qxb2 5. Bd2 Qb6 6. e4 d6 7. f4 e6 8. Rb1 Qc7 9. Bb5+ Bd7 10. dxe6 fxe6 11. Bc4 Be7 12. Nf3 Nc6 13. O-O Nxe4 14. Nxe4 d5 15. Bxd5 exd5 16. Nc3 Be6 17. Ng5 Bxg5 18. Nb5 Qd7 19. Qh5+ g6 20. Qxg5 O-O 21. c4 Bf5 22. Rbe1 d4 23. h3 a6 24. Na3 Rae8 25. g4 Bd3 26. Rxe8 Rxe8 27. Rf2 b6 28. f5 Qe7 29. f6 Qf7 30. Qf4 Re6 31. g5 Ne5 32. Qg3 Be4 33. Bf4 Nd3 0-1

3...gxf6

Most often played, although 3...exf6 does almost as well.

4 d5

The only move which allows white to retain an advantage.

4...Qb6

Here is the point of black's play. He hits the weakened pawn on b2.

5 Qc1

5 Qc1 is the overwhelmingly favorite move here. 5 Nd2 led to an odd game in Muhren-Eriwch(2000), in which black plays 5...Qxb2, giving up his queen for sufficient material compensation:  1. d4 Nf6 2. Bg5 c5 3. Bxf6 gxf6 4. d5 Qb6 5. Nd2 Qxb2 6. e4 Bh6 7. Ngf3 d6 8. Rb1 Qxa2 9. Bb5+ Nd7 10. Nc4 a6 11. Ra1 axb5 12. Rxa2 Rxa2 13. Qb1 Ra4 14. Ncd2 Rb4 15. Qa2 Ne5 16. Ke2 O-O 17. Rb1 Ra4 18. Qb3 Rb4 19. Qa2 Ra4 20. Qb3 Nxf3 21. gxf3 Rd4 22. Rg1+ Kh8 23. Nf1 Bd7 24. Ne3 b4 25. Rd1 Bb5+ 26. c4 Bxe3 27. cxb5 Rxd1 28. Qxd1 Bf4 29. Qa4 Bxh2 30. b6 Be5 31. Kd3 Rg8 32. Kc4 Rg1 33. Qa8+ Kg7 34. Qxb7 Rc1+ 35. Kd3 b3 36. Qd7 h5 37. b7 b2 38. b8=Q c4+ 39. Ke2 b1=Q 40. Qxb1 Rxb1 41. Qh3 Rb2+ 42. Kf1 c3 43. Qxh5 Bf4 44. Qg4+ Bg5 0-1

5...f5!

This inhibits white's e2-e4, and also opens up the long diagonal for the black king's bishop.

 6. c4 Bg7 7. Nc3 d6 8. e3 Nd7 9. Qc2 Nf6 10. Bd3 Bd7

Black can ignore the white threat on the f5-pawn, since 11 Bxf5 Bxf5 12 Qxf5 Qxb2 wins for black.

11. Nge2 e6 12. O-O h5 13. dxe6 fxe6 14. Nf4 Bh6 15. Rfd1 O-O-O 16. Ng6 Rh7 17. e4 fxe4 18. Nxe4 Rf7 19. a4 Nxe4 20. Bxe4 Bg7 21. Rd2 Bd4 22. Nh4 Bc6 23. Nf3 Rg8 24. Nxd4 cxd4 25. b4 Rg4 26. Re1 Rfg7 27. g3 h4 28. Kg2 Rxe4 29. Rxe4 Rg4 30. f3 Bxe4 31. fxe4 hxg3 32. hxg3 Qxb4 33. Rxd4 Qc5 34. Qd3 Kc7 35. Qd1 Rg5 36. Qd3 Qe5 37. c5 Rxg3+!

Black wins a pawn and simplifies to a queen-and-pawn endgame. Even though white's remaining pawns are isolated and weak, it still takes black 42 more moves to nail down the win, an indication of how tough queen-and-pawn endgames are to win.

 38. Qxg3 Qxd4 39. cxd6+ Qxd6 40. Qg7+

Naturally white will do all he can to avoid the trade of queens, while black will try to force a queen trade.

Kc6 41. Qc3+ Qc5 42. Qb3 Qg5+ 43. Kf3 Qh5+ 44. Kg3 Qe5+ 45. Kf3 Qh5+ 46. Kg3 Qe5+ 47. Kf3 b6 48. Qc4+ Kb7 49. Qb4 Qh5+ 50. Kg3 Qe5+ 51. Kf3 Qh5+ 52. Kg3 Qc5 53. Qb3 Qe5+ 54. Kf3 Ka6 55. Qb4 Qc5 56. Qb3 Qh5+ 57. Kf4 e5+ 58. Kg3 Qg5+ 59. Kf2 Qf4+ 60. Kg1 Qc1+ 61. Kg2 Qc6 62. Kf3 Ka5 63. Qd5+ Qc5 64. Kg4 Kxa4 65. Qd7+ b5 66. Qd1+ Ka5 67. Qd8+ Kb4 68. Qd2+ Qc3 69. Qd6+ Ka5 70. Qd8+ Ka4 71. Qd1+ Ka3 72. Qd6+ b4 73. Qa6+ Kb2 74. Qxa7 Qd4 75. Qh7 b3 76. Kf5 Kc3 77. Qh3+ Kb4 78. Qf1 b2 79. Qa6 Qd7+ 0-1  Dal Borgo-Geirnaert(2008)