Flank Opening (Zukertort Opening)

1. Nf3 is the third most popular initial move. It is highly flexible and often transposes into lines better known through other move orders, though some independent lines are possible. White reckons that Nf3 will almost certainly be a useful move sooner or later, whereas every pawn move is an irrevocable commitment, so 1. Nf3 keeps White's options open.

This means it is a useful transpositional tool. White can feel out how Black wishes to play then transpose into their preferred line. For example, a player who hates facing the queen's gambit declined, but doesn't mind the Dutch defence might play 1. Nf3 and only follow with 2. d4 if Black plays 1...f5.

Because 1. Nf3 controls the e5 square, 1...e5? would be quite bad. Therefore White can use this move order to avoid certain continuations with ...e5: if they wish to play the classical Nimzo-Larsen attack (1. b3 d5) but avoid the modern line (1. b3 e5); or a symmetrical English (1. c4 c5) but not a reversed Sicilian (1. c5 e5); they may choose to start with 1. Nf3.

Black's main way to play is to deny White 2. e4 with either 1...Nf6 or 1...d5. This leads to a number of transpositions and some more independent lines.

1...d5 takes space in the centre and prevents White from playing 2. e4?. The main replies are:

• 2. d4, which often leads to the Colle system or the queen's gambit by transposition;
• 2. g3, the king's Indian attack, otherwise seen in the French defence;
• 2. c4, the Réti, one of the most "independent" lines after 1. Nf3;
• 2. b3, the classical variation of the Nimzo-Larsen.
• 2. d3, with the idea of Nbd2 and e4, the old Indian attack.
• If 2. e4? is played anyway, this is the Tennison gambit, otherwise reached from the Scandinavian defence 1. e4 d5 2. Nf3?.

1...Nf6 is the most common reply in high-level chess. Black also avoids making a committing pawn move. Chief replies are:

• 2. d4, often transposing either to an Indian defence or to a 1. d4 d5 opening.
• 2. c4, transposing into the English opening,
• 2. g3, again with the idea of Bg2 and the king's Indian attack.

1...c5 looks to prevent 2. d4 instead. This invites White to transpose into the Sicilian defence with 2. e4, or the symmetrical English with 2. c4.

1...e5? has a name, the Ross gambit, but just loses a pawn immediately. If played anyway, it's sometimes with the idea of 2. Nxe5 Nc6?! 3. Nxc6 dxc6, called (for whatever reason) the Walrus.

1...Nc6, called the black mustang defence, invites White to transpose to normality with 2. e4 e5. However, it doesn't prevent 2. d4 because the d4 square will immediately be protected by White's queen.

When Indian chess master Moheschunder Bannerjee's games with John Cochrane were published in the 1850s in Britain, they introduced ideas on flank and fianchetto openings from Indian chess (such as the "Indian defence") to European chess, and included the earliest games with 1. Nf3.^[1]

Johannes Zukertort (1842―1888) was a master chess player, known for competing against Wilhelm Steinitz in 1886 in what is considered to be the first "official" World Chess Championship. He employed 1. Nf3 in some of his games in his 1880 match against Samuel Rosenthal^[2][3][4] and used it intermittently from then on.

Depending on who you ask, 1. Nf3 is the Zukertort and the continuation 1...d5 2. c4 is the Réti, for Richard Réti, or 1. Nf3 is the Réti and 1. Nf3 d5 2. c4 is the Réti gambit.

1. Nf3