A good choice from Hikaru. Black takes central space and after the obvious
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g1f3  3... d7d5  4. b1c3  4... c7c5 The Semi-Tarrasch is becoming more common nowadays, particularly now that people have found that the 5...cxd4 line is pretty good at forcing a draw. 5. e2e3 This move is well known to be what White plays when he is trying to avoid theory and just get a game, but Hikaru was clearly well prepared. 5... b8c6  6. a2a3  6... d5c4  7. f1c4  7... a7a6  8. c4d3 This is uncommon. 8... b7b5  9. d4c5 The computer seems to think White has a little pull here. I don't really buy it. Normally, for White to be better in this symmetrical structure, he should have better coordination (i.e. a knight on d2 vs. a knight on c6, for example). Even then, it tends to be pretty thin. With all the pieces on the same squares as well as all the pawns, it is hard to believe Black is not totally fine. 9... f8c5  10. b2b4  10... c5e7  11. e1g1  11... c8b7  12. c1b2  12... e8g8  13. c3e4 According to the machine, this move is best. But this is a very bad sign for White- it leads to mass exchanges in a symmetrical position. 13... f6e4  14. d3e4  14... f7f5  15. e4b1  15... d8d1  16. f1d1  16... f8d8  17. b1a2  17... g8f7 This was the position on the board when I woke up and first checked the games, and I thought it was already all but over. Somehow it is hard to imagine it not ending in a draw, and particularly hard to imagine someone as strong as Hikaru losing, but credit goes to Ding for finding ways to create little imbalances and putting Black's position under some pressure. 18. h2h4  18... h7h6  19. d1c1 Now, all of a sudden, Rxc6 is a threat and Nd4 would be an idea as well. 19... e7d6 The first step in the wrong direction. 20. c1c2 With the not-so-subtle intention of Rac1 coming next, when the pressure on the c-file is a bit annoying. The bishop on d6 is not a great piece and should have been exchanged for its superior counterpart on b2. 20... c6e7  21. f3d4  21... b7d5  22. a2d5  22... e7d5  23. a1c1 Now, the open d-file is clogged and not wildly useful, and White has full control of the open c-file. This should be holdable for Black, but it is definitely a bit unpleasant. 23... d8d7  24. d4b3  24... d6e7 Black aims to trade off the dark-squared bishops, correcting his earlier error, but it's a little too late for that. The weakened c5-square beckons. 25. h4h5  25... e7f6  26. b2d4 