Ipswich moved up to second place in the Championship and consigned Southampton to their third straight defeat as Omari Hutchinson's first-half goal gave the Tractor Boys victory at St Mary's.
The high-flying Suffolk side had already had a goal ruled out for a foul in the build-up before Hutchinson pounced on a Saints defensive error to put them ahead on the half-hour mark.
Conor Chaplin hit the crossbar for the visitors shortly after and a Wes Burns effort went just wide close to half-time as Ipswich created all the chances.
Ipswich remain unbeaten on the road this season and stay within a point of league leaders Preston, while Southampton drop to 11th in the table.