Dominguez chooses the most principled line.
1. e2e4  1... e7e5  2. g1f3  2... d7d6 Almost a novelty for the world champion. This is only  the second time he has used the Philidor defense. 3. d2d4  3... e5d4  4. f3d4  4... g8f6  5. b1c3  5... f8e7 