They looked the better side for much of the second half, which was played in a non-stop downpour, and could well have won. Ipswich, who had taken an early advantage, salvaged a draw when Alex Mathie equalised midway through the second half.
Ian Marshall put Ipswich ahead in the ninth minute with a low right-foot drive after Steve Sedgley had made the opening. Ipswich then looked comfortable and Mathie chipped against the bar after 23 minutes when he spotted goalkeeper David Watson off his line.
Barnsley forced their way back into the game and went close to equalising several times before they eventually drew level nine minutes into the second half when the Dutchman Arjan de Zeeuw, a pounds 250,000 signing from Telstar, volleyed in with his right-foot from a corner by Owen Archdeacon.
In the 61st minute they took the lead when Andy Liddell forced his shot past Craig Forrest from close range.
Ipswich equalised five minutes later with a fortunate goal. De Zeeuw failed to cut out a long clearance from Forrest and Mathie slipped his ninth goal of the season past the advancing Watson.
Two goals from Colin West brought Leyton Orient only their second win in 11 Third Division matches but Rochdale were unlucky to leave empty-handed.