Newcastle were forced to hang on for a second victory in three games after Jeff Hendrick saw red in a breathless contest at St James’ Park.
The Republic of Ireland midfielder was ordered off five minutes into the second half for a needless second yellow card after tugging the shirt of Takumi Minamino, the Liverpool loan midfielder who struck a stunning debut goal to halve Southampton’s deficit before the break.
Joe Willock slid home a debut goal of his own for the hosts, before Jan Bednarek’s second own goal in four days doubled the advantage.
Miguel Almiron restored Newcastle’s two-goal lead when pouncing on a woeful clearance from goalkeeper Alex McCarthy in first-half stoppage time.
James Ward-Prowse curled in a trademark 30-yard free-kick straight after the break, before Hendrick’s rash stupidity left Steve Bruce’s side to hang on. Danny Ings’ shot struck a post as Newcastle saw out the final 15 minutes with nine men when Fabian Schar was carried off with a knee injury after all three substitutions had been used.