Rules

27. Score in a Set
a. A player (or players) who first wins six games wins a set; except that he must win by a margin of two games over his opponent and where necessary a set is extended until this margin is achieved.

b. The tie-break system of scoring may be adopted as an alternative to the advantage set system in paragraph (a) of this Rule provided the decision is announced in advance of the match.
In this case, the following Rules shall be effective:

The tie-break shall operate when the score reaches six games all in any set except in the third or fifth set of a three-set or five-set match respectively when an ordinary advantage set shall be played, unless otherwise decided and announced in advance of the match.

USTA Comment: USTA Regulations require that a tie-break be played in all sets.

The following system shall be used in a tie-break game.
Singles
i. A player who first wins seven points shall win the game and the set provided he leads by a margin of two points. If the score reaches six points all the game shall be extended until this margin has been achieved. Numerical scoring shall be used throughout the tie-break game.

ii. The player whose turn it is to serve shall be the Server for the first point. His opponent shall be the Server for the second and third points and thereafter each player shall serve alternately for two consecutive points until the winner of the game and set has been decided.

iii. From the first point, each service shall be delivered alternately from the right and left Courts, beginning from the right Court. If service from a wrong half of the Court occurs and is undetected, all play resulting from such wrong service or services shall stand, but the inaccuracy of station shall be corrected immediately it is discovered.

iv. Players shall change ends after every six points and at the conclusion of the tie-break game.

v. The tie-break game shall count as one game for the ball change, except that, if the balls are due to be changed at the beginning of the tie-break, the change shall be delayed until the second game of the following set.

Doubles
In doubles the procedure for singles shall apply. The player whose turn it is to serve shall be the Server for the first point. Thereafter each player shall serve in rotation for two points, in the same order previously in that set, until the winners of the game and set have been decided.

Rotation of Service
The player (or pair in the case of doubles) whose turn it was to serve first in the tie-break game shall receive service in the first game of the following set.

Case 1. At six all the tie-break is played, although it has been decided and announced in advance of the match that an advantage set will be played. Are the points already played counted?
Decision: If the error is discovered before the ball is put in play for the second point, the first point shall count but the error shall be corrected immediately. If the error is discovered after the ball is put in play for the second point the game shall continue as a tie-break game.

Case 2. At six all, an advantage game is played, although it has been decided and announced in advance of the match that a tie-break will be played. Are the points already played counted?
Decision: If the error is discovered before the ball is put in play for the second point, the first point shall be counted but the error shall be corrected immediately. If the error is discovered after the ball is put in play for the second point an advantage set shall be continued. If the score thereafter reaches eight games all or a higher even number, a tie-break shall be played.

Case 3. If during a tie-break in a singles or doubles game, a player serves out of turn, shall the order of service remain as altered until the end of the game?
Decision: If a player has completed his turn of service the order of service shall remain as altered. If the error is discovered before a player has completed his turn of service the order of service shall be corrected immediately and any points already played shall count.