One-on-One is a basketball game where you control either Julius Erving or Larry Bird as they face off in a game of one on one. The user can select to play until a certain score is reached or for a set amount of time. On offense, the player can rotate to avoid their rival, take a shot from distance, or move in close for special slam-dunks. When defending, you can try to steal the ball or jump up to block a shot. If you succeed with a particularly good setup, you'll get a slow-motion replay.
Gameplay involves trying to score points by moving around the court, taking shots, and avoiding your opponent's attempts to steal the ball or block your shots. The game also features special moves such as slam-dunks, which can be performed when close to the basket. If you break the backboard, an irate janitor will appear on the screen to clean up the mess.