When the CPU turns into a super star when they fall behind in Mario Kart or a sports game. NBA JAM was notorious for that.
Which difficulty setting were you playing NBA JAM on? It's easy to lose focus in that game and I know the CPU does take advantage of that too. Sometimes it's a focus issue with me. if I start winning I start to get board then I stop my focus and then the CPU starts to get better as I lose focus.
But I usually win on easy with most sports game if I don't lose focus. On harder difficulty the CPU sometimes preys on your boredom. The trick with any sports game is to never lose focus while playing and to never feel sorry for the computer/opponent when it's losing
I don't care what anyone says most sports games AI are even hard on the easiest setting, it also take lots a practice and mental endurance to get good. I feel comfortable when I have lots of time.
But in short games it's usually vary hard for me to win in any sports game if I don't have enough time to play the game.