Southampton impressively outplayed and outworked Watford to secure a 2-0 victory that should signal the end of their poor run.
They were likely only one or two further defeats from becoming serious contenders for relegation, but on an evening when Watford were as poor as the hosts were intense, goals in each half from Shane Long and Dusan Tadic took Southampton into 12th place and within two points of their underwhelming visitors.
Matt Targett, playing as a wing-back, received possession on the left wing before curling an accurate, 17th-minute cross into the penalty area towards Long, from where the forward neatly headed beyond goalkeeper Heurelho Gomes and inside the right post.
Pressure had been building on Koeman, but as if to highlight Southampton's poor run had reached its conclusion and that he remained firmly in control, the manager substitutedSadio Mane for Dusan Tadic and was almost instantly rewarding with a goal.
Controlling possession after Davis' header, Tadic ran into Watford's penalty area, created space, and classily finished low beyond Gomes from in front of goal in the 73rd minute.