Scott Malone's fourth-minute goal against his former club proved sufficient to secure only a second win in 16 Championship contests for the Lions, who inflicted a fourth consecutive defeat on the hosts, after Frazier Campbell hit the crossbar from the penalty spot.
An uplifted Rowett said: "We were on a poor run of form and it's been disappointing after doing well last season and starting well this one and maybe we had gone away a bit from what we are good at to try to be a better team.
"Huddersfield's home form has been fantastic and they have really unpredictable patterns of play.
"They drag you in areas you don't want to be in, but our defensive shape was spot on. We took a few gambles with the team, playing Ryan Leonard at right centre-half and he's probably only played there once before, but we wanted a bit more pace there and he did excellently.
"Ben Thompson also gave us more aggression in midfield. We scored a good, well-worked goal that Scott finished well and you then look to see if you can get it right defensively and maybe go and get another goal.
"We couldn't do that but we did get it right defensively apart from once for the penalty.
"I think the penalty was a bit soft, but I can see why the ref gave it and you're then thinking this could spoil all the hard work, but we got fortunate and they only had one shot on target all game, because our discipline was superb and the determination phenomenal.
"That was pleasing because I don't think we have shown enough aggression and desire recently and, if we take our foot off the gas, we find it very hard to win games."
Carlos Corberan admitted that his Huddersfield team lacked potency after failing to net at home for the first time since the opening day of the season.
He said: "We had a target to get three points but, unfortunately, we did not do everything we needed to do to make that happen. They started the game quickly and we conceded an early goal to make things complicated.
"We did not defend well at the start, but we have had two penalties in the league now and not finished them well.
"We also lost a bit of control in our passing and did not create enough chances, which is something we need to improve, because the only two chances we created in the second half were from set-piece situations.
"Millwall worked a lot in their defensive half and, when things are compact, you need to open more space on the pitch, but we did not break the last line with our passes."