Well, maybe GM Baburin's Houdini likes the idea of 13...Nf4 but my Houdini 4 doesn't, or at least not as much as either 13...Nf6 [+0.10] or 13...c5 [+0.18] at d=27 after about 22 minutes of analysis (it ranks 13...Nf4 as its 3rd best move, evaluating it at [+0.32]). Perhaps if I had let it run longer it would have evaluated and ranked 13...Nf4 higher. I don't know how long GM Baburin let his Houdini run or what version of Houdini he was using.

On the other hand, Stockfish 5 evaluated 13...Nf4 as its top move as early as d=25 after less than 2 minutes of analysis, but it alternated between 13...Nf4 and 13...Nf6 as its suggested top move until I stopped the analysis after about 30 minutes at d=33. At that time it was evaluating 13...Nf4 as its top move at [-0.34], with 13...c5 as second best at [+0.19] and 13...Nf6 as third best at [+0.25]. So it is possible that Stockfish would change its move rankings again if I let it run longer, but I really have no basis for thinking that.

Finally, Komodo 8 did not evaluate 13...Nf4 as Black's top move (at [0.00] until d=24 and more than 30 minutes of analysis, with 13...Nf6 as #2 [+0.07] and 13...c5 as #3 at [+0.25]. Who knows how it would have evaluated 13...Nf4 if I had let Komodo run longer?

Therefore, in my usual style, this is how I would summarize the engines' assessment of their top 3 moves, sorted by descending Ratings Adjusted Average:

Black's Houdini Komodo Stockfish
Move d=27 d=24 d=33 <St.Avg> <RAdj.Avg>

13...Nf4 [+0.32] [+0.07] [-0.34] <[+0.02]> <[+0.01]>

13...Nf6 [+0.10] [0.00] [+0.25] <[+0.12]> <[+0.11]>

13...c5 [+0.18] [+0.25] [+0.19] <[+0.21]> <[+0.21]>

And here is a summary of how the 3 engines ranked the moves, without regard for the value of the evaluation.

Black's Houdini Komodo Stockfish
Move d=27 d=24 d=33 <Avg>

13...Nf6 1 1 3 <1.7>

13...Nf4 3 2 1 <2.0>

13...c5 2 3 2 <2.3>

Even when I enter the moves 14...Nxg2 15 Kxg2 a5 manually, 16 minutes later it is still showing a slight advantage for White with 16 a4

Granted this is only at 26 depth, so there may be horizon issues, but it is easy to see how Aronian's seconds could miss that there was buried treasure.

I have thought that looking at the evaluation trends might provide a clue. If multiple engines agree as to what the top move is (and provide similar continuations) or if the difference between the evaluation of the top line and the others is increasing, then the position is stable and the evaluations probably correct and the analysis can be stopped. But if multiple engines are showing different evaluations and each engine's top 3 moves are changing from ply to ply, then the position is unstable and the analyses need to be run longer until a stable position is reached.

Of course, a stable position might never be reached or the time to advance one ply might become impractically long. That would also be an indication that the analysis must be stopped and that forward sliding is necessary.

I agree. For the most part, the eval you get in the first five minutes is going to stay the same, but there are positions, like this one after 13...Nf4, where the engine will give you no clue for well past that time that there is anything other than drawing chances with 14 Nd2-f3 Nxg2

How to identify those positions is really difficult. Here someone (Cheparinov?) went on the original voyage of discovery, and found that the eval changes when you slide forward with the moves ...a5 and ...Ra6

I would be really interested if Stockfish and Houdini register 14...Nxg2 immediately as a good move. That, as you suggested, would give a clue that the position was different than most, and would at least mark the position as worth looking at longer.

I noticed just analyzing with Komodo that it settled on 16 a4 very quickly and held to that opinion up to 28 plys with evals near 0.00 plus or minus .10, but then jumped to -.55 and rose. Was it because it took that long to see the effect of the last piece-the rook on f8- to become involved?

Or was it that 14...Nxg2 was only one of some 50 some moves it had to search?

Caught like a trout in the opening.

- Wesley So (after 14...Nxg2!)

I wrote that harsh criticism at 5:20am. I was working early on Saturday.

Now that I have had more than 20 minutes to mogitate upon that pun, I realise its superb merits.

So sue me! Sorry, couldn't resist one more. If you don't like So puns, maybe you will like this instead:

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simply 27..Qxe3! since 28.fxe3 Rd2+ is fatal.

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<ajile> Very nice continuation that shows the base weaknesses in White's position