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, 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.

"It underscores how seriously we regard any suggestion of corruption in our sport. The BHA team are industry leaders in this area and their expertise, knowledge and resource will be invaluable to our investigation."

British online bookmaker Betfair voided all bets on Davydenko's defeat by Martin Vasallo Arguello at the Sopot Open in Poland. Davydenko won the first set but retired with a foot injury when trailing 2-1 in the deciding set.

Betting patterns

"Betting patterns before the market were as expected for this match," a Betfair spokesman said, explaining the turn of events that raised their suspicions.

"But before a ball was struck Arguello the world no.87 had become favourite. Davydenko's odds continued to drift and after he won the first set 6-2 he drifted even further. At that point it was clear something was not right."

Betfair, which allows clients to bet even after the match has started, said that $7.3m of bets had been accepted on the match.

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

The ATP set up an Anti-Corruption programme in 2003, binding all professional players and their support staff to a stringent set of rules regarding betting.

Since then no players have been found to have broken the rules.