Kevin Nugent refused to "paper over the cracks" of his Under 23s side's performance despite a 3-0 victory over Cardiff City on Monday afternoon.
Goals from Isaac Olaofe and George Alexander (2) eventually eased The Lions to another Professional Development League victory, but the manager couldn't hide his disappointment with certain aspects of his team's play in the first two-thirds of the match.
The win keeps Millwall's Under 23s in the top two of the Southern Section of the Professional Development League.
"Most games that end up comfortable don't start in the same way," Nugent told millwallfc.co.uk. "For 70 minutes, we weren't great. If anything, I thought we were quite average. In the last 20 minutes, however, we took our chances and put the game to bed - it could've been more. But, I'm not papering over the cracks with regards to the first 70 minutes.
"We want to win every game. It's difficult to be disappointed when you lose 3-0, but we've set some really good standards this season and I don't think we matched them today. It's good, however, that we're up the top of the table and the players are developing, too."
Junior Tiensia put pen-to-paper on his first professional contract last week, and Nugent praised the left-back, as well as stating how the gap betwen age groups is beginning to close.
"It's good to get Junior tied up to the club. He's got potential, but as a young lad there are parts of his game that needs to improve. We'll be working on those with him.
"We feel we're closing the gap [between the Under 23s and first-team] a little bit, but their performances can be up and down, so we've got to make sure we've got that level of consistency in them."