Kyle Walker-Peters' stunning strike was enough to give Southampton all three points against Bristol City, a result that moved Saints up to fourth in the Championship.
The right-back unleashed the curling shot into the top corner two minutes into the second half after a frustrating first 45 minutes for the hosts.
Tommy Conway had missed a golden chance to put City ahead just before the break with a one-on-one with Saints keeper Gavin Bazunu that was saved.
The win means Southampton stretch their unbeaten run to 10 games while the Robins stay in mid-table after falling to a first defeat under Liam Manning.