Under-fire officials at the rain-hit US Open defended their handling of the scheduling chaos in the face of criticism from players on Wednesday.

Andy Roddick and Martina Navratilova spoke out as more heavy rain caused severe delays at the season's final Grand Slam for the third day running.

Roddick welcomed the impromptu opening of indoor practice courts at Flushing Meadows but only with a thinly-veiled attack on the United States Tennis Association (USTA).

The American fourth seed's comments followed a withering assessment of the Open's organisation by Martina Navratilova as the "poorest scheduling" she had seen in her Grand Slam career.

But Arlen Kantarian, chief executive of the USTA professional tennis division, told reporters: "I don't see that we could have possibly done anything differently at this point.

"I have heard a lot of discussion about (covers for the court during rain). But I don't recall a session where a (cover) would have cut down on (preparation) time (when rain clears).

"Also, hindsight on having a roof is easy to have -- we have said we are looking at the possibility of installing a roof over a show court in the future.

"So it's not to say that given the experience we've had that we're not going to look at everything (in the coming months).

"But everyone is working hard. They are doing everything possible.

"The tennis community has pulled together over the last day and a half."

With players increasingly frustrated, the USTA freed up three indoor courts on Wednesday for the competitors to practice on.

NAVRATILOVA CRITICISM

The indoor hall had been converted into an activities centre aimed at younger fans -- called "Smashzone" -- since the start of the Open on August 25.

"It's obvious that (the change) had to happen," Roddick told USA television network.

"The Smashzone is great for kids but when it takes priority over players practising, it's a little questionable."

Navratilova, the 18-times singles Grand Slam champion, believes the majority of players are unimpressed with the organisation.

"This is the poorest scheduling I've ever been part of in any grand slam," the 46-year-old, who is still in the women's doubles competition, told the New York Times on Wednesday.

"If you ask the other players, they would say the same thing but they haven't played in as many as I have."

For the second year running, the wet weather has exposed the set up at the U.S. Open.

First round matches are spread out over the first three days, with critics arguing the USTA should aim to complete the first round in two days.

Top seed and world number one Andre Agassi was unhappy after the referee's office decided to reschedule other matches ahead of his rain-hit third-round encounter with Yevgeny Kafelnikov earlier in the tournament.

Most players have been faced with a myriad of time and court changes to their matches over the last three days.

The rain has left organisers trying to play catch-up in a desperate bid to finish the tournament on the advertised day of Sunday, September 7.