Blake was initially told he had missed out on the quarter-finals

The American finished tied with Juan Del Potro and Evgeny Korolev in the round-robin stage after Del Potro retired with Blake leading 6-1 3-1.

The ATP said Blake should qualify as he was on course when Del Potro retired.

But 24 hours later, ATP chief Etienne de Villiers admitted: "Clearly, I was wrong to intervene."

I regret that I got involved, that I overruled a supervisor, and I regret this storm in a teacup Etienne de Villiers, ATP chief executive

Blake had needed to win his final match in straight sets with the loss of no more than five games to secure a quarter-final place, and the suggestion was that Del Potro's retirment had denied him that chance.

De Villiers stepped in, saying: "James was within just a few games of winning this match comfortably to advance."

However, 24 hours later the ATP chief executive said: "I was contacted late at night my time and did not fully understand the issues being discussed and I made a judgment call on what seemed fair.

"However, I understand that judgment calls are not part of the rule book and I must abide by the rules, as must everybody else in the circumstance.

"I apologise to James for giving false hope and to Evgeny for the confusion. I regret that I got involved, that I overruled a supervisor, and I regret this storm in a teacup."

Following a similar situation in Buenos Aires, the round-robin format that was introduced at the turn of the year faces an uncertain future.