Having posted the worst start to a Premier League season by any side after 21 games, the Saints knew a positive display was needed against Nuno Espírito Santo’s high-flying team.
However, true to form, it was the hosts who dominated the opening exchanges, and their early pressure was rewarded with a breakthrough in the 11th minute when Elliot Anderson rifled in a low strike from range for his first goal in Forest colours.
Ivan Juric’s side posed a threat at the other end with some neat attacking play but the Tricky Trees delivered a sucker punch shortly before the half-hour mark.
Callum Hudson-Odoi capitalised on a heavy touch from Jan Bednarek on the edge of the box before sweeping a clinical effort beyond Aaron Ramsdale into the bottom corner.
Forest continued to stamp their authority on proceedings and a third goal duly arrived before half-time, with Chris Wood heading home from Ola Aina’s inviting delivery - the New Zealander’s 14th league goal of the season.
Faced with a daunting three-goal deficit, Southampton were fortunate not to fall further behind in the early stages of the second half when Anthony Elanga saw a sharp strike thwarted by Ramsdale.
Grateful for that reprieve, the visitors pulled one back through Bednarek, who diverted Lesley Ugochukwu’s effort beyond Matz Sels in the Forest goal.
The hosts thought they’d restored their three-goal cushion shortly after, only for Nikola Milenkovic’s header to be ruled out for a Wood offside.
With time ticking into the final 20 minutes, Nuno looked to rest several of his key players as the Tricky Trees closed in on a comfortable three points.
However, the visitors set up a nervy finale when substitute Paul Onuachu rose highest in the box to convert Mateus Fernandes’ corner.
That gave the Saints hope of salvaging an unlikely point, but Forest held firm in the closing stages to extend their unbeaten run across all competitions to nine matches (W8, D1).
As for Southampton, Juric becomes the first permanent manager at the club to lose their first five league games.
Flashscore Man of the Match: Elliot Anderson (Nottingham Forest)