Chess Openings Lab
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Semi-Slav Defense: Main Line

The Semi-Slav Main Line is 5.Nf3, where White develops the last knight and keeps every option open. Black must now pick a setup: ...Nbd7 for the Meran families, ...a6 for the accelerated plan, or ...Bd6 with an early capture on c4.

Moves
1.d4 d5 2.c4 c6 3.Nc3 Nf6 4.e3 e6 5.Nf3
ECO
D45, D46
Engine
+0.18 · level (Stockfish 17.1, depth 20)
Played
2,208 games in our lichess sample
White scores
55.7%

Key ideas for both sides

White

  • Against ...Nbd7, Qc2 and Bd3 prepare e4; this is the engine's top line and keeps a small edge.
  • Against ...a6, b3 keeps c4 protected by a pawn so ...dxc4 does not gain time.
  • Against ...Bd6, Bd3 lets Black take on c4 and play ...b5, but the d3 bishop is well placed.
  • Castle short and aim for e4, the main central break in every one of these setups.

Black

  • 5...Nbd7 is the most common choice and keeps both ...dxc4 with ...b5 and the ...e5 break available.
  • 5...a6 is a useful waiting move that prepares ...b5 and can lead to the Accelerated Meran.
  • 5...Bd6 develops first and can take on c4 later with ...b5 to gain time against the bishop.
  • Do not hurry ...dxc4 before White moves the f1 bishop; let White spend a tempo first.

Plans and pawn structure

All the main setups share the c6, d5, e6 pawn triangle and a White pawn on e3. White's plan is usually Bd3, castling, and the e4 break. Black waits for the bishop to land on d3 and then takes on c4 to gain a tempo with ...b5, or prepares ...e5. In the Meran structures, Black plays ...Bb7 and ...c5 to free the bishop and challenge d4. Move order tricks matter here, so know which setup you want.

What the engine plays from here

Stockfish 17.1 at depth 20 rates the position +0.18: level. Its three top choices for Black:

  1. +0.18 5...Nbd7 6.Qc2 Bd6 7.Bd3 O-O 8.O-O
  2. +0.23 5...a6 6.b3 Bb4 7.Bd2 O-O 8.Bd3
  3. +0.31 5...Bd6 6.Bd3 dxc4 7.Bxc4 b5 8.Bd3

Pawns, from White's side.

How it scores on lichess

2,208 rated lichess games reached this position; White scored 55.7%.

under 120060.8%
1200–159958.6%
1600–199953.1%
2000 and up57.6%

Light: White wins. Grey: draws. Dark: Black wins. About the sample.

Where it goes next

How to play against it

With Black, choose 5...Nbd7 if you want the main Meran world, or 5...a6 if you prefer a less common route. Avoid early ...Bb4, which loses time after Bd2 and a3. With White, keep your plan simple: Bd3, Qc2, castle and e4.

Other lines with this name

The lichess opening list also files these lines under the same name, though they reach a different position: 1.d4 d5 2.c4 c6 3.Nc3 Nf6 4.e3 e6 5.Nf3 Nbd7 6.Bd3; 1.d4 d5 2.c4 c6 3.Nc3 Nf6 4.e3 e6 5.Nf3 Nbd7 6.Qc2 b6 7.b3 Bb7 8.Bd3 Be7 9.O-O O-O 10.Bb2.

Questions

What are the moves of the Semi-Slav Defense: Main Line?

The Semi-Slav Defense: Main Line starts 1.d4 d5 2.c4 c6 3.Nc3 Nf6 4.e3 e6 5.Nf3. Its ECO code is D45, D46.

Is the Semi-Slav Defense: Main Line good for White?

Stockfish 17.1 rates the position +0.18 at depth 20, which is level. In 2,208 lichess games from our sample, White scored 55.7%. A main road for both sides, suited to players who like structure-based play and are willing to learn a few move orders.

What is the main idea of the Semi-Slav Defense: Main Line?

White completes development with Nf3 and keeps all options. Black chooses between ...Nbd7, ...a6 or ...Bd6, each aiming either to take on c4 and play ...b5 or to free the game with ...e5.

What should Black play next?

The engine's first choice is Nbd7, with a6 and Bd6 close behind. 5...Nbd7 is flexible: it supports ...e5 and keeps ...dxc4 with ...b5 ready once White commits the bishop.

Updated October 2026. Sources and method.