It's a disappointing defeat for the Reds in Suffolk as Jonas Knudsen's second half header is enough for the hosts.
Danish full back Knudsen popped up after 54 minutes to glance home an inswinging corner which condemned Barnsley to defeat in a game they were probably dominating prior to the goal.
Reds Head Coach, José Morais made one enforced change to the side that beat Sheffield United at the weekend, George Moncur was sick and so in came Adam Hammill.
It was Morais' men quickest out of the blocks and with less than five minutes on the clock a Hammill corner was met by the onrushing Kieffer Moore, but the former Ipswich striker's header cannoned back out off the Town crossbar.
Despite the bright start, it became a real scrappy affair with neirther side playing at their best, but the Reds always looked the more likely to grab a goal in the first half.
25 minutes in and Brad Potts played a lovely one-two inside the box with Hammill, but the former's powerful shot from the left on the angle flew into the side netting.
Ipswich carved out a great opportunity eventually when after Martyn Waghorn's clever ball, Bersant Celina found himself one-on-one with Reds 'keeper Adam Davies, but he blazed his effort well over the Reds bar.
Lloyd Isgrove had been quiet on the right flank but he scored on the stroke of half time, only to see the linesman lift up his flag for offside, after he'd tucked home from close range after a great knock-down by Moore.
HALF TIME: Ipswich 0-0 Reds
Five minutes into the restart and Moore flashed a header wide of the post from Hammill's corner, and within a minute, the hosts showed Barnsley how to do it.
After Davies failed to prevent a corner, the resulting set-piece was whipped in at pace to the near post, and Knudsen got ahead of everyone to glance home the ball using the pace on it to beat Davies, the ball dropping into the far corner for 1-0.
Ryan Hedges replaced Lloyd Isgrove on 56 minutes as Morais looked to get the Reds back into the contest which became scrappy once more with the home side using all the tricks in the book to slow down play.
Tom Bradshaw then entered the fray on 64, on for Hammill. But the Reds were struggling to find a way through a stubborn Ipswich back three.
But with 20 minutes remaining the goal scorer Knudsen absolutely scythed down Bradshaw as he was about to enter the box, with the referee only giving a booking to the Dane despite it looking a shocking tackle.
Nothing came of the free-kick and the home side were now creating the better chances as they picked the Reds off on the counter.
Stevie Mallan replaced the injured Zeki Fryers with 10 left to play.
There was a late Barnsley flourish, plenty of balls into the box and balls not quite dropping, but it was a disappointing night at Portman Road and the Reds will now have to regroup ahead of what looks an even bigger clash with Bolton Wanderers at Oakwell on Saturday.
FULL TIME: Ipswich 1-0 Reds
Davies, Yiadom, Jackson, Lindsay, Fryers (Mallan 81), Gardner, Potts, Isgrove (Hedges 56), Bradshaw (Hammill 64), Moore, McBurnie.
Unused: Walton, Pinnock, Mahoney, McCarthy.