Ruy Lopez 5.d4 exd4 6.Qxd4 and White is in . After 4...dxc6, the obvious 5.Nxe5 is weak, since 5...Qd4 6.Nf3 Qxe4+ 7.Qe2 Qxe2+ leaves White with no compensation for Black's bishop pair. There are two principal lines after 4.Bxc6 dxc6. In the late 19th and early 20th centuries, Lasker had great success with 5.d4 exd4 6.Qxd4 Qxd4 7.Nxd4. Since then, better defences for Black have been developed, and this line is considered to slightly favour Black. Jon Jacobs wrote in the July 2005 "Chess Life" (p. 21): "A database search (limited to games longer than 20 moves, both players FIDE 2300+) reveals
Open Game and preparing for d2–d4. Black's most common reply is , which usually leads to the Ruy Lopez (3.Bb5), Italian Game (3.Bc4), or Scotch Game (3.d4), though 3.Nc3 Nf6 (the Four Knights Game), often played in the late 19th to early 20th century, or, less commonly, 3...g6 or ...Bb4, (the Three Knights Game), are other possibilities. If Black instead maintains symmetry and counterattacks White's center with then the Petrov's Defense will usually result, though White can avoid the extensive theory of the Petrov by playing 3.Nc3 if he wishes. The Philidor Defence, (2...d6), largely fell out of use after World War