Deuce and Advantage

When a game reaches 40-40, standard scoring requires a player to win by a margin of two points rather than simply the next point. Winning the point immediately after deuce gives that player "advantage". This means informally, "ad in" if the server has the advantage or "ad out" if the returner does. If the player with the advantage wins the following point, they win the game. If they lose it, the score returns to deuce and the sequence repeats until someone wins two points in a row. This is what allows a single game to theoretically extend indefinitely, and long deuce battles of many advantages back and forth do occur, though they are relatively rare.

The deuce-and-advantage structure is one of the defining features that separates traditional tennis scoring from no-ad formats. It rewards players who can perform well under repeated close-game pressure rather than settling a game on a single point. Momentum within a deuce sequence is often discussed by commentators and coaches. This is because a player who has just saved several advantage points may carry a psychological edge into the next one, even though each point technically starts even.