How do you treat 1. e4, c5 2. c3, Nc6?

I cannot find any opening theory about the answer 2.Nc6 in the Alapin, suggesting that it is an obviously bad, or at least uninteresting move. I am looking for an expert vision or standard strategy how to play this with white. Who can help me?

In blitz games I see it 3 out of 4 occasions being played.

3.d4, of course. This is the reason white played 2.c3, and since Black did not bother to prevent it, you should play this move.

Why is 3.Nf3 so overwhelmingly popular then in the databases?  d4 seems so much more logical and straightforward, but there must be a reason most play Nf3.

EDIT: Or maybe the Opening Explorer here just has the stats reversed.  Another database shows the logical d4 to be much preferred.  Sigh...

Further EDIT: As does a third.  Great, one more part of chess.com I no longer trust.

2...Nc6 is a straightforward attempt to take the fight to the d4 square.  If it were good, it would be one of the main responses to the c3 Sicilian.  The fact that it's a sideline might suggest something...

Thank you all for your answers!

GM's do not play bad moves like 4...e5?, nor they reply to them with another bad move such as 5.d5?

Are you sure you have understood the basic positional rules?

Simply 4...e5? 5.dxe5 Nxe5 6.Nc3 (or just 6.Nf3) leaves Black with a sick backward d-pawn, reduced central control, and zero compensation for that.

If Black wants to play 2...Nc6!? against the Alapin (maybe because they play 2...Nc6 against 2.Nf3) they MUST follow up against 3.d4 with 3...d5, more than likely transposing to a variation of the 2...d5 line after 4.exd5 Qxd5

But after 2...Nc6!? 3.d4 cxd4?! 4.cxd4 it's a little late for 4...d5 because of 5.Nc3 (this line can also be reached from the Slav Exchange, with a little "help" from Black).  And if he doesn't play 4...d5 he's going to get steamrolled by White's d5 push

Actually it's a pretty good point... Why is it a sideline? It's not bad at all... black can go down 2 paths that seem ok to me... 4... e6 and 5... d5 and white will choose to either push e5 or play with an isolated pawn.

1.e4 c5 2.c3 Nc6 3.d4 cxd4 4.cxd4 e6 5.Nc3 d5 6.e5 is a superior Advance French for White, because Black is committed to the early c-pawn exchange which gives White a natural square on c3 to bring the QN out.  Normally if the c5 and c3 pawns remain in place for a while, White has difficulty bringing this knight into the game as Nd2 interrupts the defense of d4..

I prefer steamrolling Black with my QP: 5.d5.  Once Black fails to play 3...d5, his position is decidedly inferior.

There I fixed it for you: http://pgntools.nfshost.com/comment_remover.html

Ahhh: I did not even consider the isolated pawn!

 My point is that I wish it were a sideline: Sveshnikov's great book (The COMPLETE c3 Sicilian) does not mention it at all, not even among the sidelines, yet I am put out of book on move 2 the majority of times. Thanks to the answers, I now  think I "understand the basic positional rules".

2...Nc6 3.d4 d5 reults to a pretty playable position for Black- but the simple question is: what Black is to gain by not playing 2...d5 at once? The only thing he achieves is losing some flexibility, the knight on c6 sometimes proves himself to be oddly placed. I think the best way to justify it is the "modern" variation 4.exd5 (4.dxc5 is playable, but nothing special) Qxd5 5.Nf3 Bf5, which is quite trendy recently.

Well it isn't that superior... just because the tension in the c5 break is released doesn't mean there's no play in the position. You can still put pressure on d4 or play for the typical f6 break and both seem to lead to equality...

It doesn't look like White gets a whole lot out of 5.d5 after 5...Bb4+ 6.Bd2 Qe7+.

As for the above sequence, 7.Be3 is premature and 7.Nc3 Nf5 8.a3 seems more reliable as 8...Qb6 is comfortably met by 9.Na4, and 8...f6 by 9.g4.  I never claimed White's advantage was huge, but he is quite comfortable here as opposed to the ordinary French Advance move order which is full of obstacles for White.

 It took only a few days for me to realise the difference! Thanks for this tip.

Last night I completed a game where my opponent played 2 ..Nc6 in the Sicilian Alapin. I vaguely knew that was an uncommon move (Nf6 is played often here), but for a 1200 rated player it is not easy to find the right response. I managed to kick the horse around a bit, and ultimately won the game. But I would say that 2.. Nc6 for Black is OK against a beginner/intermediate player. As a side note, I didn't look up any of these moves as we were playing, but my opponent accused me of doing so in the chat.

White tried play for the center and develop the lighter pieces. Black's strategy was to pin these pieces to the King, but he couldn't prevent White from castling kingside. I think White came out of the opening better because Black's light-squared Bishop was stuck, but the opening of the game was fairly even. Black lost because of a blunder at move 12, and not because 2 ..Nc6 was bad.

Nc6 is only good followed by d5, transposing back into a Barmen Defence line and then black just equalises easily.

Black is known to be doing pretty well here as they are better developed and the queen can't be kicked due to c3. 2. ...d5 is the normal order though.

I found an interesting play; Bd4 with the idea to put it in c2 in the next move, i found a couple of games with that move, you might want to check them out.

https://www.365chess.com/opening.php?m=6&n=22104&ms=e4.c5.c3.Nc6.Bd3&ns=3.3.37.239.22104