Taylor Harwood-Bellis netted the only goal as Southampton triumphed at QPR to make up ground on the top two.
The on-loan Manchester City defender volleyed in from close range just before half-time to stretch fourth-placed Saints' unbeaten run to 15 games.
Rangers, who remain third from bottom, created chances but were unable to fashion an equaliser.
Russell Martin's side held on to secure the three points despite a late red card for midfielder Shea Charles.
QPR looked the more threatening of the sides during the opening 45 minutes, with Ilias Chair's bold attempt from the halfway line giving Saints goalkeeper Gavin Bazunu a scare before it sailed just over.