To defend the h-pawn.
1. e2e4  1... c7c5  2. g1f3  2... e7e6  3. c2c3  3... d7d5  4. e4d5  4... d8d5  5. d2d4  5... g8f6  6. b1a3 A touch of  Tiviakov. The Groningen-based former Russian GM won a decisive game  against Sutovsky to become European champion some years ago in this line. 6... b8c6  7. c1e3  7... c5d4  8. a3b5  8... d5d7  9. b5d4  9... f8d6  10. d4c6 Van Foreest spoils the opponent's pawn  structure. 10... b7c6  11. e3d4  11... c8b7  12. f3e5 This is the difference. The knight is getting to a much better position with tempo. 12... d7e7  13. e5c4  13... d6c7  14. d1b3  14... b7a6  15. b3a3 Also a good maneuver. White can best  exploit the pawn weaknesses in the endgame. 15... e7a3  16. c4a3  16... a6f1  17. e1f1  17... c7b6  18. d4f6  18... g7f6  19. f1e2 Almost by force, a complex endgame  arose. Van Foreest has clearly better pawn structure, while Yu owns the  better minor piece. This simple fact should have made the Chinese GM more  alert about possible future trades. 19... h8g8 An inaccuracy. 20. g2g3  20... e8c8  21. a3c4  21... c8c7  22. a1d1  22... d8d5  23. d1d3  23... h7h5  24. h1d1  24... g8d8 A mistake. Yu is not careful about the possible trades. 25. c4e3  25... b6e3  26. e2e3  26... d5e5  27. e3f3  27... e5d5  28. d3d5  28... c6d5  29. d1d4 This is  the endgame I mentioned before. The weak pawns on a7 and h5 are causing  Black constant headaches. 29... d8b8  30. b2b3  30... c7d6  31. f3e3 