Instead of blindly attacking at all times, the AI opponents are more relaxed when the ball is still in your half and tend to not run around so much until you get closer to their half. This definitely makes for more realistic soccer, although it also promotes time play to a certain degree. If you're ahead one goal, simply keep the ball in your half and slowly play back and forth. The ref should whistle after a while, but he doesn't. Naturally, this isn't a concern in the multiplayer mode.
Allied players behave more intelligently and allow for much better wing play.
Another AI improvement concerns the goalie behavior. In addition to the fully automatic goalie support seen in previous installments in the series, FIFA 99 also features semi-automatic controls. Not only can you pick up the ball if the goalkeeper has trapped it with his feet, but you can also take control of the goalie at the touch of a button if you're worried that the computer might mess up. On the control side, the developers finally tightened things up with interruptible motion capture animations. Previously, turns weren't interruptible, which meant if you started turning around, you had to complete the motion before changing direction again.