My apologies to readers waiting for some serious analysis - I still have some things to say about 1.a3:
1.a3 e5 2.e4 (Dia)
I suspect this move will come as a surprise to many players. We now have a position that could as well arise from 1.e4 e5 2.a3, which at first seems rather meaningless in a set of openings where we have learned that rapid development is essential.
This is natural and probably best. It is debatable whether the extra a-pawn move has any significance in the reversed King’s gambit arising after 2...f5!?. What is certain is that this is an unlikely move to encounter unless your opponent is a regular King’s Gambit player. One of the relatively few practical examples is 3.exf5 Nf6 4.Be2 (4.g4!?) 4...Bc5 5.Nf3 d6 6.d4 exd4 7.Nxd4 0–0 8.0–0 Bxd4 9.Qxd4 Bxf5 with fairly equal chances in Anbuhl-T.Kristiansen, Gausdal 1981.
Now we enter the so-called Mengarini Opening (which normally would arise after 1.e4 e5 2.Nc3 Nf6 3.a3). It can be considered a reversed version of the Open Games where the Ruy Lopez obviously is ruled out. It seems unlikely that the extra move will make a reversed Latvian with 3.f4?! a tempting option.
With 3...Bb4?? (a reversed Spanish) out of the question, one might expect 3...d5 (a reversed Scotch) to be Black’s best try, as Kasparov has made a case for this being White’s only serious alternative to the Spanish. However, it turns out that after 4.exd5 Nxd5 5.Qh5!, may be a major obstacle. In the parallel line 1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Qh4, White has the promising pawn sacrifice 5.Nb5 (or possibly a delayed version with a later Nb5). As this obviously is not an option here, 5...Nc6 6.Bb5 may be quite unpleasant for Black, e.g. 6...Qd6 7.Ne4 Qe6 8.Nf3 Bd6 9.Nfg5 Qg6 10.Qf3 f5 11.Nxd6+ Qxd6 12.d4 0–0 13.Bc4 Nce7 14.Bd2 exd4 15.0–0–0 h6 16.Rhe1 with a clear advantage to White in Czarnota-Korosciel, Poraj 2003.
3...Bc5 4.Nf3 d6 obviously must be sound. One of the more high-powered games continued 5.h3 Nc6 6.d3 a6 7.g3 0–0 8.Bg2 Be6 9.0–0 h6 10.Kh2 d5 with equal chances, Wahls-Brueckner, German Cht 1990.
4.Nf3 d5 (Dia)
This probably is critical.
a) 4...Bc5 5.Nxe5! is good for White, and one of the basic ideas behind the Mengarini, e.g. 5...Nxe5 6.d4 Bd6 7.dxe5 Bxe5 and now:
a1) 8.Bd3 0–0 9.0–0 Re8 10.Ne2 d5 =+ Levitsky-Steinitz, Moscow 1896.
a2) 8.Nb5 a6 9.f4 axb5 (9...Bxb2 10.Bxb2 axb5 11.e5 Qe7 12.Bxb5) 10.fxe5 Nxe4 11.Qg4 d5 12.Qxg7 +/- Molander-Van Hoolandt, Gausdal 2002.
b) 4...a6 makes some sense; Black reclaims his right to be Black. The game Gunsberg-Zukertort, London 1887 casts some doubt about the playing level at the time: 5.d4 exd4 6.Nxd4 g6 7.Bg5 h6 8.Bh4 Bg7?? 9.Nxc6 bxc6 10.e5 g5 11.exf6 Qxf6 12.Bg3 when White was winning.
c) 4...d6 allows White to take the initiative in the centre with 5.d4 exd4 6.Nxd4 when Black seems unable to take advantage of White’s tempo-loss:
c1) 6...Nxd4 7.Qxd4 Be7 8.Bc4 0–0 9.0–0 Kh8 10.Bg5 Ng4 11.Bxe7 Qxe7 12.f4 (12.Nd5) 12...Be6 13.Be2 += Carlsen-Potapov, Peniscola 2002.
c2) 6...Be7 7.Be2 (7.Bc4 0–0 8.0–0 Re8 9.h3 Nxd4 10.Qxd4 Nd7 11.Nd5 Nb6 12.Nxe7+ Qxe7 = Gullaksen-Simonsen, Torshavn 2003) 7...0–0 8.Be3 Re8 9.Qd2 Nd7 10.0–0–0 Bf6 11.f4 Nb6 12.g4 Bd7 13.g5 Bxd4 14.Bxd4 Nxd4 15.Qxd4 += Motwani-Winants, Belgium 2001
d) 4...g6 is a reversed version of Glek’s Four Knight’s line. White’s most entertaining move is 5.Nxe5!?, to which I may return in a later entry. It has however limited theoretical significance as Black after 5...Nxe5 6.d4 Nc6 7.d5, can return the piece with 7...Bg7! 8.dxc6 bxc6 and reach exactly the same position as after 5.d4 exd4 6.Nxd4 Bg7 7.Nxc6 bxc6.
Also 5.exd5 Nxd5 6.Bb5 Nxc3 7.bxc3 has been tried, but White has been unable to prove any advantage: 7...Bd6 8.d4 exd4 9.cxd4 0–0 10.0–0 Bg4
a) 11.c3 Qf6 12.h3 Bxf3 13.Qxf3 Qxf3 14.gxf3 Ne7 15.c4 Nf5 16.Be3 Nh4 17.f4 c6 =+ Bae-Porat, Port Erin 2003
b) 11.Be3 Ne7 12.h3 Bh5 13.Bd3 Nd5 14.c4 Nxe3 15.fxe3 c5 = Golubovic-Z.Szabo, Budapest 1995
5...Nxe4 may be better:
a) 6.Qe2 Nxc3 7.Qxe5+ Qe7 8.dxc3 Bd7 1/2–1/2 Gullaksen-A.Moen, Stockholm 2004.
b) 6.Nxe5 Qf6 7.Nf3 Be6 8.Qe2 Nxc3 9.dxc3 Bd6 10.Bg5 Qg6 11.Bd3 Qh5 12.Bf5 Ne5 (12...0–0!) 13.Bxe6 fxe6 14.Nxe5 Qxe2+ 15.Kxe2 Bxe5 = Djurhuus-A.Moen, Gausdal 2002
The position has become semi-closed. I doubt White has any advantage, but there should be plenty of opportunities to outplay a weaker opponent. One typical game is G.Welling-Reimer, Dinard 1986:
6...Nxe4 7.d3 Nf6 8.Nxe5 Qd5 9.Bxc6+ bxc6 10.Nf3 c5 11.0–0 Bd6 12.c4 Qb7 13.b4 += Glek-Zaja, Austria 2005.
7.d3 Bd7 8.0–0 g6 9.c3 dxc3 10.bxc3 (Dia)
White is better developed, better co-ordinated and has more pawns in the centre. But with accurate play it is still possible that Black could hang on.
10...Nd8?! 11.a4 c5 12.d4 Bxb5 13.axb5 Bg7 14.dxe5 Ng4
14...Nxe4 15.Re1 0–0 16.Nf4 Nxc3 17.Qb3 is no better.
15.Bg5 Qc7 16.Nf4 Nxe5 17.Nd5 Nxf3+ 18.Qxf3 (Dia)
Black's position is just too bad. 18...Qd7 19.Rfd1 and 18...Qd6 19.Rfd1 are just as hopeless.