Ruy Lopez Open Variation [FEN ""]
1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Nxe4


Why is 6. Re1 not played, prefer players 6. d4 only? Please answer with explanation and variations so that it could help all players.
After 6.Re1, black equalizes comfortably after 6....Nc5, as he wins the bishop pair. For example, 7.Bxc6 dxc6 8.Nxe5 Be7 9.d4 Ne6 10.c3 0-0.

Instead, 6.d4! is the main line, after which 6....b5 7.Bb3 d5 8.dxe5 Be6 is almost forced for black. The resulting position is the tabiya of the Open Spanish.



      [StartPly "10"]

      [FEN ""]
      1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Nxe4 6.Re1 (6.d4! b5 7.Bb3 d5 8.dxe5 Be6) Nc5 7.Bxc6 (7.Nxe5 Be7) dxc6 8.Nxe5 (8.d4 Ne6) Be7 9.d4 Ne6 10.c3 O-O