The decisive mistake.
1. d2d4  1... g8f6  2. c2c4  2... g7g6  3. f2f3 Vachier-Lagrave is faithful to his Grunfeld Defense. Every now and then he has to face this dangerous variation that leads to very complicated positions. 3... c7c5 One option that Black has is to transpose to a Benoni or King's Indian Saemisch Variation. Incidentally, a question remains for those who are experts in opening nomenclature: when Black plays c5 in the King's Indian, should we call it a Benoni $2 4. d4d5  4... d7d6  5. b1c3  5... e7e6  6. e2e4  6... f8g7  7. g1e2  7... a7a6  8. a2a4 This is useful to prevent …b7-b5 after an exchange of pawns on d5. 8... d8e7 A new move. To be honest, I don't quite understand what advantage Black has in delaying the inevitable moves that are the exchange on d5 or 0-0. 9. d5e6 Aronian decides to exploit Black's move order. Taking the knight to g3 or f4 and then completing development is also playable. 9... f7e6 This capture is necessary, since it's not easy to defend the d6-pawn after 10. c1f4 Forcing Black to advance the pawn to e5 in order to protect d6. 10... e6e5  11. f4g5 The knight now goes to d5, gaining a tempo by attacking the queen. White's position is comfortable and easier to play, although the advantage is not as big as I thought. 11... b8c6 The right move, preparing to take the knight to d4. 12. c3d5  12... e7d8  13. e2c3  13... c6d4  14. f1d3  14... e8g8  15. e1g1  15... c8e6 The last few moves from both sides were quite logical and now White needs to choose a plan. 16. c3e2 It's logical to exchange the powerful knight on d4. 16... d4e2 A bit passive. It would be better to take the knight on d5 or play a6-a5, fixing the queenside. In any case, it1s better to let White exchange knights on d4, so that Black has a passed pawn and the d-file cannot be exploited. 17. d3e2  17... f8f7  18. d1d2  18... d8f8 Not an ideal plan, to say the least. Something went very wrong with Black's opening play. 19. d5b6 An excellent move, preserving the knight and getting ready to open the position with b2-b4. Black's problem is that he has no counterplay. Imagine how Vachier-Lagrave, with such an aggressive style, was feeling without being able to play an active move. 19... a8d8  20. a1d1  20... h7h6  21. g5e3  21... f7c7  22. b2b4 A dream position for Aronian. White plays totally risk-free. 22... c5b4  23. d2b4  23... c7c6  24. a4a5 Securing the strong knight on b6. 24... h6h5  25. b6d5 The knight returns to the center. 25... d8d7  26. e2d3 Another great move, preparing Bc2-a4. The computer also suggests stuff like the surprising g2-g4, but why complicate the game when you have total control $2 26... d7f7  27. d3c2  27... g8h7  28. e3f2 A difficult move. Aronian is in no hurry, and although I don't understand exactly what the benefits of this move are (maybe preventing h5-h4 $2), Black doesn't have much to do anyway. 28... c6c8  29. d5b6  29... c8d8  30. c4c5 A good positional decision. It's true that White exchanges Black's backward pawn on d6, but he is the one benefiting from the opening of the d-file. 30... d6c5  31. f2c5  31... f8g8  32. d1d8  32... g8d8  33. f1d1  33... d8g8  34. c5e7 Preparing the unpleasant Rd8. 34... g7h6 Freeing the g7-square for the queen, while activating the bishop. 35. b6d5 It's funny how the knight goes back and forth to b6 and d5. 35... e6d5  36. e4d5  36... g8c8 Vachier-Lagrave finally activates the queen, although maybe it's too late. But this is the best chance. 37. c2b3 