Make sure you are in Standard Season or Elimination. Custom Season and Elimination and Exhibitions won't work. From there you simply have to keep the opponent from scoring in the game. It's not that hard on lower ego. Vary your pitches and where you place them. The main thing to watch out for is random home runs which the CPU likes to do. If it doesn't come in the first game or two, it should come eventually as you can end up playing some teams where players are in funks or injured as well as entering games with your pitcher in the zone which makes him more effective.