NEIL Harris said it was a "tough decision" to drop David Forde before the 0-0 draw with Scunthorpe at Glanford Park.
Harris handed Jordan Archer his first league start for the Lions and was rewarded when the keeper made a string of important saves.
The former Tottenham keeper produced arguably the best of them when he denied Paddy Madden in a one-on-one early in the first half.
Harris said: "Every decision is tough. Picking the team isn't always easy, as I'm finding out.
"I'll get some wrong during the season and I'll get a lot right.
"I'll focus on the positives, which was that the 11 players and the boys that came off the bench were terrific.
"Jordan has made a couple of good saves and they missed a penalty, but we had lots of chances as well.
"Steve Morison hit the post in injury-time and that summed it up for both benches, that it was going to be a nil-nil."
The Millwall artsandhealth.ie/ventolin/ boss altered his formation for the game, opting to pick a three-man midfield as the Lions kept their first clean sheet of the season.
Ben Thompson also made his full league debut after two impressive appearances as a substitute against Coventry and Barnsley.
"Ben is one of our top young players," Harris said. "He has done really well in the last two games coming off the bench, but just because you do well off the bench you can't presume they'll do really well starting.
"You have to be patient and pick them at the right time, and we got that right today with Ben.
"It helps having the experience of Shaun (Williams) and Jimmy (Abdou) in there and we went with the three because at the moment teams are playing three-man midfields against us.
"We went with energy in there and control in the middle of the park, and I also wanted to play with three strikers."