The doubling is natural and strong. Karjakin probably believed that he will be in time to stop it:
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g1f3  3... d7d5  4. b1c3  4... f8e7  5. c1g5  5... b8d7  6. e2e3  6... h7h6  7. g5f4  7... e8g8  8. g2g4 The Shabalov/Shirov way! Especially pleasing in rapid and blitz  games. 8... c7c5  9. g4g5  9... h6g5  10. f3g5  10... c5d4  11. e3d4  11... d5c4  12. h1g1 White has a nasty initiative for the pawn and  Karjakin needs to play both carefully and energetically. An oxymoron, I  know. 12... f6d5 The knight was a very important defender and should  have not left his place. 13. d1c2 A simple but difficult to parry mate-in-one threat. 13... e7g5 The only move. 14. f4g5  14... f7f6  15. g5h6 Now Dubov's initiative is more than obvious. 15... f8f7  16. f1c4  16... d7b6  17. c4e2 First of all White is creating a threat. 17... f6f5 Black does not want to let the enemy queen too close. 18. e1c1  18... d8h4  19. h6g5 Dubov was not afraid to sacrifice earlier; why  would he be now? 19... h4f2  20. c2d2  20... c8d7 After this obvious move White's attack plays  itself. 21. d1f1 The point! Dubov opens a second highway to... refer to AC/DC to  know where. 21... f2h2  22. g1h1  22... h2d6 