LONDON (Reuters) - The Association of Tennis Professionals (ATP) has asked the British Horseracing Authority (BHA) to assist its investigations into irregular betting in a match involving Russian world number five Nikolay Davydenko.

In a statement on Friday, ATP executive chairman Etienne de Villiers said: "We are committed to a thorough, fair and comprehensive ATP investigation and our decision to involve the BHA, as well as employing independent investigators, is testimony to that commitment.

Betfair, which allows clients to bet against each other even after the match has started, said that $7.3 million of bets had been placed and accepted on the match.

"Normally for a match like that it would have been around one million dollars," the spokesman said.

Davydenko said he had been upset by the controversy surrounding the match and that he had never received any contact from anyone regarding the throwing of a match.