SOUTHAMPTON 1 (Wright-Phillips 85), UNITED 0
Southampton: Bialkowski, Baird, Lundekvam, Pele, Skacel, Idiakez (Belmadi 65), Guthrie, Viafara (Wright-Phillips 55), Surman, Jones, Rasiak (Best 89). Subs: Davis, Crainie.
United: Ankergren, Richardson, Heath, Marques, Elliott, Blake (Foxe 37), Kishishev, Thompson, Lewis (Kandol 86), Healy (Sa 66), Cresswell. Subs: Stack, Moore.
Referee: Tony Bates (Staffs)
Dennis Wise was forced into making changes to his starting line-up, following the departure of Lubo Michalik, recalled by Bolton, and injury to left-back Michael Gray.
Robbie Elliott and Rui Marques were recalled to the side while Alan Thompson also took his place at the heart of the midfield after shaking off injury.
Roared on by a magnificent travelling support, United started on the attack and won a first corner of the game within the first 90 seconds.
That set-piece was cleared, but when United came storming forward again moments later, Richard Cresswell had a penalty appeal waved away after taking a tumble under pressure in the Saints box.
Southampton also looked sharp going forward, Jhon Viafara started well on the right, and Matt Heath reacted well to deal with a couple of early crosses from the flank.
United continued to defend with confidence, and Southampton's first half-chance didn't come until the midway point in the half when Grzegorz Rasiak headed over the top.
And on 30 minutes, Saints long-serving skipper Claus Lundekvam followed suit when he headed a great chance over the bar.
United's response was immediate, though, and Cresswell headed a Thompson free-kick over.
But Wise's men were dealt a bitter blow shortly after the half-hour mark when Thompson was controversially handed a red card.
The referee had awarded the hosts a free-kick, following a foul on Viafara, and Thompson appeared to be dismissed after attempting to restrain the Saints man from clashing with Eddie Lewis.
Referee Tony Bates consulted with his assistant before producing a straight red card.
The decision sparked angry scenes as the United players protested, and bizarrely, stewards moved onto the pitch to surround Mr Bates.
United boss Wise, who was clearly unhappy with the decision, immediately sacrificed Robbie Blake and replaced him with the defensive Hayden Foxe.
The sending-off raised temperatures on the field and in the moments leading up to the interval, challenges flew in thick and fast from both sides.
And in first half stoppage time, the home side came within a whisker of snatching the lead when Kenwyne Jones headed against the upright.
It looked like being backs to the wall stuff for 10-man United as Southampton attempted to make their numerical advantage count in the second period with a couple of early raids.
Jones had the best opportunity on the hour-mark when he was afforded a free header, but he could only guide it straight into the arms of Ankergren.
It wasn't all one way either - United were showing great character - and David Healy tested home goalkeeper Bartosz Bialkowski with a stinging effort from the edge of the box.
Wise re-shaped his side with Marques taking over the anchor role and on 66 minutes the hard-working Healy was replaced by Armando Sa as the manager looked for fresh legs for the closing stages.
Within 30 seconds of the change, United fashioned out another opening and Foxe sent an overhead kick fizzing over the top.
Along with Heath, Foxe was equally dominant at the other end as United showed no sign of wilting under some intense spells of pressure.
When the hosts did force an opening, their finishing or final ball wasn't up to scratch, and while the Southampton fans grew restless, the 3200 away supporters, sensing a terrific away point, roared their side home.
There was another scare on 80 minutes when Rasiak got up well at the far post, but he could only guide his header wide of the mark.
Breaking quickly, it took a fantastic block from Pele to deny Radostin Kishishev from putting United in front after some great movement.
But hearts were broken six minutes from time when Saints substitute Bradley Wright-Phillips hooked the ball onto the underside of the bar and into the net.
It was cruel on the 10 men of United who had defended magnificently and, against all the odds, had held firm against a team desperately pushing for a Play-Off place.