Full-time score from Portman Road
Millwall's fantastic unbeaten run finally came to an end as goals from DJ Campbell (2) and Daryl Murphy condemned Kenny Jackett's men to their first defeat in 14 games.
The Lions had not lost a match since Brighton eked out a 2-1 win at The Den way back on 22nd September.
But pitched against an Ipswich Town side resurgent following the appointment of former Lions boss Mick McCarthy, something was going to have to give.
Unfortunately it proved to be Millwall's proud unbeaten run as Jackett's men, trailing 1-0 at the break to Campbell's 36th-minute opener, were hit twice more through Murphy (50mins) and then a 64th-minute penalty from loanee striker Campbell.
"Chris Wood's goal in the first half looked bang onside, so we could have been 1-0 up," bemoaned Jackett.
"Overall, we had problems with Murphy and DJ Campbell. Their front two were a handful. One got two goals, the other got one and our guys didn't hit the target when we've been ruthless up front.
Ipswich played with good intensity today and in the first half the game could have gone either way but they got the edge."
Lions boss Jackett made two changes to the team that drew with Charlton last week bringing in fit-again Liam Trotter and James Henry for Josh Wright and Liam Feeney, both of whom dropped to the bench.
It was Ipswich who caused an early scare in the first minute when Murphy sprinted down the left, only to rush his cross and watch his mishit delivery drop on the roof of David Forde's goal.
Millwall had the ball in the back of the net after four minutes when Shane Lowry's sliderule pass found Chris Wood, but his crisp finish was ruled out for offside by what must have been a matter of inches.
At the other end Henry's attempted backheel to Adam Smith was easily intercepted by Murphy on seven minutes and the latter's hanging cross was headed over by Lee Martin.
The Lions settled into their stride with both full-backs increasingly providing good support. Right-back Smith embarked on a couple of exhilerating runs down the flank, the second of which started with an outrageous dummy on the half-way line. His subsequent pass sent Andy Keogh clear in space and his cross, intended for Henry and Wood who were both lurking in the danger zone, was cleared by Luke Chambers for a corner.
Millwall looked to have the measure of their opponents as they produced some delightful passages of play that created a handful of chances too.
Wood was left holding his head in his hands after sending a free header over from six yards after Henry's freekick was flicked on by Lowry and the Ipswich goal led a charmed life just past the half-hour mark too.
Home keeper Stephen Henderson denied the visitors with a fabulous double save, first parrying Trotter's rasping shot at full stretch and then, when Keogh touched the loose ball into Henry's path, the keeper pushed his goalbound effort round the post to thwart Millwall again.
Those saves proved the turning point of not only the half, but the game, and just three minutes later Ipswich found themselves ahead. Aaron Cresswell used the time and space afforded to him on the left to pick out Campbell, who nipped in behind Danny Shittu and sidefooted home from barely three yards with a typical predator's goal.
Having looked quite comfortable, Jackett's men found themselves in a rare position - certainly in recent games - of going in at half-time a goal down and the big question was quite how they would respond.
Certainly the last thing Millwall wanted was to concede a second, but within five minutes of the restart that is exactly what happened.
Campbell was again involved, this time wriggling past Shittu and picking out Murphy who rifled the ball into the roof of the net giving Forde no chance.
The last time Jackett's men faced a 2-0 deficit was at Crystal Palace in October and The Lions dug in to share the spoils.
On that occasion there was, ofcourse, the helping hand of having a numerical advantage against Palace's 10-men. But against Ipswich's XI, it was going to be a big ask to get anything from this game.
And moments after introducing Dany N'Guessan and Josh Wright for Chris Taylor and Jimmy Abdou, that task became virtually impossible with Lowry penalised for handball and Campbell making no mistake from the penalty spot.
Thereafter The Lions huffed and puffed but simply could not find their attacking rhythm and it could have been even worse in the dying moments when Martin broke clear of a static backline, saw his chance as Forde rushed out of his goal and despatched a delightful lob that Shittu somehow scrambled off the line.
It's not how hard you fall down, but how fast you pick yourself up. And with the visit of Play-Off chasing Leicester City to The Den next Saturday, The Lions will need no greater incentive to get back to winning ways at the first opportunity.
Henderson, Cresswell, Chambers, Campbell (Chopra, 84mins), Edwards, N'Daw, Martin (Barnett, 84mins), Drury, T.Smith, Orr (Hewitt, 88mins) , Murphy. Subs not used: Loach, Higginbotham, Emmanuel-Thomas, Carson.Ipswich Town:
Campbell (36mins, 60mins pen), Murphy (50mins)Scorers:
Forde, A.Smith, Lowry, Abdou (Wright, 54mins), Shittu, Beevers, C.Taylor (N'Guessan, 54mins), Trotter, Keogh, Wood, Henry. Subs not used: M.Taylor, J.Smith, Osborne, Malone, Feeney.Millwall:
: Wood (34mins), Beevers (81mins)Bookings
17,318 (away 1,109)Att: