Both teams soon found their stride following an insipid opening to proceedings at a rain-soaked Portman Road, with Ipswich striker David McGoldrick the recipient of the game's first chance.
The 25-year-old found himself with the necessary time and space inside the area, but his tame effort was easily gathered by goalkeeper Tom Heaton.
The league leaders soon began to replicate the form which has seen them ascend to the summit of England's second tier, as full-back Kieran Trippier galloped down the flank but nobody was on hand to convert his teasing pass across the face of goal.
However, Mick McCarthy watched on as his team came perilously close to opening the scoring on the brink of half time.
The Tractor Boys managed to retain their momentum following the interval, as Luke Chambers should have headed the hosts into the lead, only for his back-post effort to be thwarted by Heaton.
McCarthy's men struggled to build on their earlier dominance, and fell behind 11 minutes from the end.
The hosts threatened to restore parity, and came close in the dying stages, only for Shackell to produce a last-gasp block to deny Jay Tabb to preserve his team's position at the top of England's second tier.