In the third case, there is nothing to do, once the material advantage is obtained, but to submit to the opponent's attack for a while, and once it has been repulsed to act quickly with all your forces and win on material. A good example of this type of game is given below.
From the Havana International Masters Tournament, 1913.
(Ruy Lopez) White: J. R. Capablanca. Black: D. Janowski.
I have passed over the game lightly because of its difficult nature, and because we are at present concerned more with the opening and the middle-game than we are with the endings, which will be treated separately.