Once you bought Player Cam from the shop, try cursor lock on the goalkeeper and play from 4 to 6 stars. Note: 6 stars is unlockable by purchasing it from the shop. 4 to 6 stars results in more penalties in game. A PK shootout works as follows. If the PK taker is shooting the ball to the striker's right side, you will control the keeper to try and save the shot by pressing the Left Analog-stick Right as well. However, if you are in an actual game, and you locked on the goalkeeper in Player Cam, once the striker starts the run up and the camera returns to Player Cam if the striker is shooting to the keeper's left side, press the Left Analog-stick in the opposite direction to the dive. For example, if you want to dive to the left in a game, press the Left Analog-stick Right.
