Did Aronian make a mistake in the opening against Anand in round 1 of the FIDE Candidates 2014? Here is the game 

[Event "FIDE Candidates 2014"]
[Site "Khanty-Mansiysk RUS"]
[Date "2014.03.13"]
[Round "1.3"]
[White "Anand, Viswanathan"]
[Black "Aronian, Levon"]
[Result "1-0"]
[WhiteElo "2770"]
[BlackElo "2830"]
[ECO "C88"]
[Opening "Ruy Lopez"]
[Variation "closed, 7...O-O"]
[EventDate "2014.03.13"]
[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Be7 6. Re1 b5 7. Bb3 O-O 8. h3 Bb7 9. d3 d5 10. exd5 Nxd5 11. Nbd2 Qd7 12. Nxe5 Nxe5 13. Rxe5 Nf6 14. Re1 Rae8 15. Nf3 Bd6 16. Be3 Re7 17. d4 Rfe8 18. c3 h6 19. Ne5 Bxe5 20. dxe5 Rxe5 21. Qxd7 Nxd7 22. Red1 Nf6 23. c4 c6 24. Rac1 R5e7 25. a4 bxc4 26. Bxc4 Nd5 27. Bc5 Re4 28. f3 R4e5 29. Kf2 Bc8 30. Bf1 R5e6 31. Rd3 Nf4 32. Rb3 Rd8 33. Be3 Nd5 34. Bd2 Nf6 35. Ba5 Rde8 36. Rb6 Re5 37. Bc3 Nd5 38. Bxe5 Nxb6 39. Bd4 Nxa4 40. Rxc6 Rd8 41. Rc4 Bd7 42. b3 Bb5 43. Rb4 Nb2 44. Bxb5 axb5 45. Ke3 Re8+ 46. Kd2 Rd8 47. Kc3 1-0


So I am wondering. The Spanish Marshall should give black plenty of compensation for the sacrificed pawn. Yet, black did not seem to get much play after white grabbed the pawn. Did black make a mistake in the opening or later in the middlegame (endgame)? Thanks!
Aronian played two sub-optimal moves in the middlegame - 16...Re7 and 18...h6. At each of these moves, the better move as per analysis by Houdini (depth 25 and above) was Nd5! (Houdini even prefers 17...Nd5, but 17...Rfe8 is not bad)

So his "mistake" was missing the opportunity to play Nd5, and instead playing 16...Re7 (which seems to be the major culprit) and 18...h6. If, instead, he had used the Nd5 idea, he could have equalized on move 16, and might have had better chances for equality if he had used it on move 18. 

   [FEN "4rrk1/1bpq1ppp/p2b1n2/1p6/8/1B1P1N1P/PPP2PP1/R1BQR1K1 w - - 0 16"]

   1. Be3 Re7? (1... Nd5! 2. Bd2 c5=) 2. d4 Rfe8 (2... Nd5!? 3. Bd2 Nf4 4. Bxf4 Bxf4 
   5.  a4+=) 3. c3 h6?! (3... Nd5! 4. Bd2 Rxe1+ 5. Nxe1 Nb6 6. Nc2+=) 4. Ne5! Bxe5 
   5. dxe5 Rxe5 6. Qxd7 Nxd7 7. Red1+=


Explanation for 16...Nd5!

The idea behind 16. Be3 was to play 17. d4, which would strengthen White's position and prepare the Ne5 idea. Note that White couldn't play 16. d4 because of 16...Bxf3! The Ne5 idea gives White a pleasant edge in the endgame because of the two bishops. Therefore Black should have prevented it by preventing White's d4 move. Thus, the move c5 comes to mind, which discourages d4 because of c4, trapping the bishop on b3. However, c5 can wait for Nd5, an intermediate move, which forces White to retreat the bishop and also improves the position of the knight. After, Nd5 and c5, Black is completely equal.