user8291: After 1.d4 Nf6 2.c4 e6 3.a3, what is the best reply?
Assuming that I, as Black, am a Nimzo-Indian Player, there is no hope for a Nimzo now. Would you go for 3...d5 (QGD with no particularly useful a3 move by White), or for 3...c5 aiming for a Benoni-like structure but allowing 4.d5, or with 3...b6 for a Queen's Indian structure? Or something else?
[Title "What is Black's best reply?"]
[FEN ""]

1.d4 Nf6 2.c4 e6 3.a3


user14202: According to chessTempo.com's database for over 2200 rated player games 3...c5 scores best for Black with 43% wins for Black and only 20% wins for White.
By-the-way, there is another alternative you didn't mention which is 3...d6

user33461: You can get an improved Benoni with 3...c5, but objectively, 3...d5 is the best answer to 3.a3. The strong players probably go for a Benoni transposition because they think unbalanced positions will make the win easier, but 3...d5 is the best because it instantly equalizes. White can then best go for 4.cxd5 exd5 and now black can develop its light squared bishop without any problems, as opposed to a normal Carlsbad structure without a3.

user7297: This really comes down to what you're comfortable with. Both the Benoni and the QGD are good options, precisely because of the reason you mention: a3 isn't really useful for White in those openings, so you'll be playing lines with a tempo up. According to chessgames.com, Black is already better. Which line (3... d5 or 3... c5) is better is just a matter of personal preference.
3... b6 is of course playable, and Black scores 50%, but it allows White to transpose to one of the main lines of the Queen's Indian with 4. Nf3. 

8291: <p>After <strong>1.d4 Nf6 2.c4 e6 3.a3</strong>, what is the best reply?</p>
<p>Assuming that I, as Black, am a Nimzo-Indian Player, there is no hope for a Nimzo now. Would you go for 3...d5 (QGD with no particularly useful a3 move by White), or for 3...c5 aiming for a Benoni-like structure but allowing 4.d5, or with 3...b6 for a Queen's Indian structure? Or something else?</p>
<pre><code>[Title &quot;What is Black's best reply?&quot;]
[FEN &quot;&quot;]

1.d4 Nf6 2.c4 e6 3.a3
</code></pre>
 14202: <p>According to chessTempo.com's database for over 2200 rated player games 3...c5 scores best for Black with 43% wins for Black and only 20% wins for White.
By-the-way, there is another alternative you didn't mention which is 3...d6</p>
 33461: <p>You can get an improved Benoni with 3...c5, but objectively, 3...d5 is the best answer to 3.a3. The strong players probably go for a Benoni transposition because they think unbalanced positions will make the win easier, but 3...d5 is the best because it instantly equalizes. White can then best go for 4.cxd5 exd5 and now black can develop its light squared bishop without any problems, as opposed to a normal Carlsbad structure without a3.</p>
 7297: <p>This really comes down to what you're comfortable with. Both the Benoni and the QGD are good options, precisely because of the reason you mention: a3 isn't really useful for White in those openings, so you'll be playing lines with a tempo up. According to <a href="http://www.chessgames.com/perl/explorer?node=75552&amp;move=3.5&amp;moves=d4.Nf6.c4.e6.a3&amp;nodes=10703.11482.11470.75542.75552" rel="noreferrer">chessgames.com</a>, Black is already better. <em>Which</em> line (3... d5 or 3... c5) is better is just a matter of personal preference.</p>

<p>3... b6 is of course playable, and Black scores 50%, but it allows White to transpose to one of the main lines of the Queen's Indian with 4. Nf3. </p>
