The review system already has been used at three Masters Series tournaments in North America, the U.S. Open, six other ATP Tour events and this week's Kremlin Cup in Moscow.

The Madrid Masters begins Monday and the Paris Masters starts Oct. 30.

So far, there have been 816 challenges in 274 matches, with 310 challenges backed up by the replays for a success rate of 38 per cent, the ATP said Thursday.

``I like everything about it,'' Andy Roddick said. ``I think it's great for the fans.

``I think it adds another dimension to watching it on TV.''

Each player receives two challenges a set. If the player is correct with a challenge, the player retains the same number of challenges.

If the player is incorrect, one of the challenges is lost. During a tiebreaker in any set, each player will receive one additional challenge. Challenges may not be carried over from one set to another.