Lesson
White to move. Main line: 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3 c5 5. a3 Bxc3+ 6. bxc3 b6 7. Bd3 Bb7 8. f3 Nc6 9. Ne2 O-O 10. O-O Na5 11. e4 Ne8 12. Ng3 cxd4 13. cxd4 Rc8 14. f4 Nxc4 15. f5 f6 16. Rf4 b5 17. Rh4 Qb6 18. e5 Nxe5 19. fxe6 Nxd3 20. Qxd3 Qxe6 21. Qxh7+ Kf7 22. Bh6 Rh8 23. Qxh8 Rc2 24. Rc1 Rxg2+ 25. Kf1 Qb3 26. Ke1 Qf3
White advances with e4, f4 and f5, gaining space and threatening the black king. Euwe answers with active queenside play: ...Rc8, ...b5 and ...Qb6 force White to calculate both wings instead of attacking without interruption.
The tactical turn is 18...Nxe5. After 19.fxe6 Nxd3, Black’s pieces flood the open files. Euwe permits 21.Qxh7+ because the king can step to f7 and the rook reaches h8 with decisive tempo.
The final sequence ...Rc2, ...Rxg2+ and ...Qb3–f3 turns defense into mate. The lesson is concrete counterplay: when an attack is supported by advanced pawns but underdeveloped pieces, striking the center or back rank can be faster than passive defense.