NEIL Harris believes the arrivals of Jake Cooper and Jed Wallace during January's transfer window have raised the overall level of his squad as he watched his side defeat Port Vale 2-0 on Tuesday night to stretch their unbeaten run to 12 games.
Millwall have conceded just one goal since Cooper joined from Reading – and that was on his debut at Bradford on January 21 – and kept a fifth successive clean sheet as they comfortably beat Michael Brown's side.
Cooper also scored his second goal in three games when he added to Aiden O'Brien's first-half strike after Steve Morison's missed penalty and it is now eight hours since Jordan Archer has been beaten in goal.
Shaun Hutchinson's return from injury late last year – though the former Fulham defender was again absent against Port Vale – and Cooper's arrival also allowed Harris to shift Tony Craig to left-back, where the Millwall captain has arguably played his best football this season.
And Harris feels Cooper's partnership with Byron Webster, and the work done on the training ground, has been key to Millwall improving their defensive record.
"We were letting too many goals in at the start of the season, and we worked hard, we worked hard, we worked hard on it," Harris said. "We didn't always get the rub of the green and it wasn't always individually or the back four, it was the whole team.
"We've gone back to basics. We brought young Jake in from Reading and when you bring someone in on loan you've scouted them because you think they've got ability. You hope that they fit into your style of play and create partnerships and understandings, and he has slotted in nicely between two really good experienced pros in Byron and Tony.
"And Shaun Cummings gives us that defensive element at right-back. Jed and Coops coming in has just coincided with some of our big players returning to form around the Christmas period. There was no doubt before then we had too many players out of form.
"The spirt its good, the team spirit is excellent, and the togetherness."
Millwall controlled the game against Port Vale to move to within nine points of the automatic promotion places.
Archer had just one save to make, from JJ Hooper in the first half, and Millwall could have added more goals only for Vale goalkeeper Leo Fasan, who faced 18 shots, to do well to keep out efforts from Wallace and Fred Onyedinma in the second half.
Harris was also able to bring off Morison, Onyedinma and O'Brien late on with one eye on the fifth round of the FA Cup against Leicester City this Saturday.
"I think we were dominatant and some of our football was fantastic tonight, I really enjoyed watching it," Harris said. "There were moments when we gave it away cheaply but some of our movement off the ball was excellent.
"Some of the chances we created were outstanding and I said to the players I was disappointed we didn't get four or five tonight, that was the level of performance.
"We lost our way a little bit when I made the substitutions, taking off the three boys in quick succession. We lost our guile and movement a little bit.
"But I thought we were well worthy of a clean sheet, I was delighted with that first and foremost. Attacking-wise we looked a threat all evening."