NEIL Harris came to the defence of David Martin after the goalkeeper's mistake in the last minute of normal time allowed Brighton an equaliser before the Premier League side went on to win a penalty shootout and set up a date against Manchester City in the semi-finals of the FA Cup.
Martin misjudged Solly March's free-kick in the 95th minute, seven minutes after Jurgen Locadia had scored what looked like would only be a consolation.
Harris revealed Martin was "devastated" in the dressing room after the game.
Millwall were leading through Alex Pearce's header in the 70th minute followed by Aiden O'Brien's goal 11 minutes from time.
"What an outstanding performance for 94 minutes," Harris said. "First and foremost I feel for Dave Martin because he was excellent throughout the game.
"He absolutely commanded his box, made some saves, good kicking, but he's made a slight error of judgement and it's cost us.
"He's a top pro, one of the nicest guys I've ever come across in football, as a player, coach or manager. No problem with that.
"He's devastated. He's made a mistake, he's put his hands up and said he's let the boys down. He hasn't let the boys down, he's made an error of judgement.
"He is a great character, very popular in the changing room but he has made a slight error. His error looks worse than others but if forwards are more clinical when they get their one-on-one chances, defenders make better challenges in wide areas, we get closer in the box for their first goal then the second one doesn't become a problem.
"I'm more disappointed with the first goal, I've got to be honest, the defending wasn't good enough in a wide area and in the penalty area.
"We missed two one-on-ones before scoring the first two goals so we could have been out of sight. Extra-time the keeper makes a great save but then Mahlon [Romeo] should score the rebound."
Harris had brought on defenders Shaun Hutchinson and James Meredith in the last five minutes before Brighton struck late.
Harris said: "Hindsight is wonderful. Our opportunity to win the quarter-final was at 2-0 up in the 89th minute. Would I change anything I did? No, not at all.
"The 11 players on the pitch should have been capable of seeing out a 2-0 lead with the amount of defensive players and leadership we had on the pitch.
"What you can't do is legislate for human error. At the end of the day that's what cost us."
Image: Millwall FC