Hillsborough match commander David Duckenfield has accepted his failure to close the tunnel was the direct cause of the death of 96 people in April 1989.
Giving evidence during the new inquest into the disaster, Mr Duckenfield said it had been the most difficult period of his life to admit his professional failing led to the deaths.
The officer in charge of policing at Hillsborough said that police "lost control" by 2.40pm on the day of the tragedy.
On his third day of evidence, former Chief Superintendent David Duckenfield was shown video of up to 2,000 people entering the central pens in the run up to the FA Cup semi-final on April 15, 1989.
He said: "Around 2.30 we were in a situation that wanted monitoring.
"Then we had radio difficulties and all concentration, focus was lost. By time it was restored we'd lost control."
ITV Granada reporter Andy Bonner is at the inquest:
Earlier, he said that the pens at 2.49pm looked full but at moments appeared to be enough room for people to raise their arms and chant.
Rajiv Menon QC, representing families of Hillsborough victims, asked him whether it is proper to allow the pens to fill up with people to the extent they can't move.
"I would dispute the word allow," Duckenfield said. "I have admitted my failings but I was attempting to save lives."
Hillsborough match commander accepts his failure to close the tunnel was the direct cause of the death of 96 people in April 1989.
The police match commander at Hillsborough has said he thinks there was no conspiracy about the disaster.