David Duckenfield was speaking about the events which led to the disaster at the FA Cup semi-final between Liverpool and Nottingham Forest at the Hillsborough Stadium in Sheffield.
"It was a grave mistake and I apologise profusely," the 70-year-old said, prompting gasps of horror from the victims' families who were attending the inquest in Warrington.
"Everybody knew the truth, the fans and police knew the truth that we'd opened the gates."
Duckenfield, 70, said he had "no idea" what had made him lie and apologised unreservedly to the families.
"(It is) one of the biggest regrets of my life," Duckenfield added, referring to his failure to consider the consequences of opening the gate.
"I think it's fair to say that I was overcome by the enormity of the situation and the decision I had to make and as a result of that, this is probably very hard to admit, I was so overcome probably with emotion of us having got into that situation that my mind for a moment went blank."
The Liverpool supporters were crushed to death on the terraces after entering the ground through the open gate.
The Taylor Report in 1990 concluded that the main cause of the disaster was the failure of police control.
It prompted major changes in safety standards at stadiums in Britain with perimeter fencing removed and many grounds converted to all-seater.
