Tarrasch Variation, Open System, Süchting Line

In the Süchting Line, White answers the Open System's 3...c5 with 4. c3. Instead of resolving the central tension with 4. exd5 or preparing a knight recapture with 4. Ngf3, White defends d4 with a pawn and keeps the full center. The problem is that e4 has not yet been exchanged or advanced, unlike in the Closed Tarrasch structures where c3 fits naturally. Black can use this at once with 4...dxe4 5. Nxe4 cxd4 6. cxd4. The trades leave White with an isolated d-pawn that has few defenders and must be guarded by pieces, while Black gets easy development against it. The engine's preferred moves are 4...dxe4, 4...cxd4 and 4...Nc6, and it rates the position as roughly equal.

In practice, 4...Nc6 is the most common reply. It adds pressure to d4 and keeps open the choice of capturing on e4 or d4 later. 4...cxd4 is the second choice, and 4...Nf6 is seen only occasionally. The line is a modest sideline. In online games, results are almost even, with Black very slightly ahead.