Matt Sadler, signed on loan from Watford yesterday, was handed his County debut as a direct replacement for Michael Rose who moved to Norwich City on a similar deal.
Gary Ablett's other new signing, Plymouth striker George Donnelly, had to settle for a place on the bench.
David Poole made a welcome return to the starting eleven to replace the injured Johnny Mullins.
James Vincent was expected to move to right-back with Poole playing alongside Jemal Johnson up front.
Also on the bench for the first time this season was the youth team's leading marksman, Cameron Darkwah.
Saints included former Hatter Rickie Lambert and newboy Lee Barnard, the former Southend United striker who scored twice at EP earlier this season.
Two goals inside six second-half minutes gave Southampton victory.
Rickie Lambert bundled the Saints in front on 63 after Owain Fon Williams half punched a Joseph Mills corner.
And then substitute Papa Waigo N'Diaye scored at the far post following a good cross from the right by Michail Antonia.
With Michael Raynes and Danny Swailes continuing their impressive partnership in the heart of the Hatters' defence County were very comfortable in the first half.
And they might have taken the lead on 11 minutes when Poole found space in the box and hit a powerful rising drive that Kelvin Davis did well to tip over.
Lambert then twice tried his luck from distance but each time Fon Williams was equal to the task.
The Hatters came close again six minutes before the break when a corner was cleared to Richie Partridge lurking out side the box. The winger controlled his volley bit it was too close to Davis who made the save.
And they came close again in first-half stoppage time when Danny Pilkington cut inside and was unlucky to see his shot hit Saints' skipper Jose Fonte.
After the goal Waigo N'Diaye should have added another when he carle4ssly headed a Mills cross wide of the post.
And Fon Williams made good saves from Lambert and then Antonio.
Donnelly came off the bench to pep up the County attack and the former Skelmersdale striker almost grabbed a debut goal in added time when he turned smartly and forced Davis into a fine save.

















