The Gulls lost their fourth game in five after conceding two goals in the second half at Plainmoor.
Brett Williams put United ahead in the 25th minute only for Southport to reply with goals in the 67th and 75th from Callum Howe and James Caton respectively.
Player-manager Kevin Nicholson drafted defender Ben Gerring back into the starting line-up after serving his six match ban. Lathaniel Rowe-Turner returned to his left-back berth and Giancarlo Gallifuoco continued in his new role at right-back.
Southport came out the quicker of the two sides at the beginning of the first half. The first real opportunity came in the 24th minute when Hynes’s cross-cum shot whistled past the far post. Moore may have had it covered however.
Brett Williams scored his second goal for the club, and what a goal it was. He found some space thirty-yards out, took the ball forward and found the angle to curl the ball past Southport ‘keeper Magnus Norman. It was a goal full of poise and class.
As with any opening-goal, United quickly found the confidence to knock the ball around and test Dover even further.
Defender Ben Gerring headed a corner over the bar as the first half ended.
United were well-placed to take the game to Southport in the second half, but it was the visitors that found more attacking verve after the break.
United started to create a few ‘nearly’ moments. Young over-hit his pass ever so slightly trying to find the run of Reid. Young was one of the better United players on the day, always looking for the ball and trying to get things started in midfield.
Callum Howe equalized for Southport with a lob just as United were starting to build some steam again. It wasn’t the prettiest lob ever scored, more functional than graceful, but it put Southport back on terms.
It didn’t take long for Southport to take the lead. James Caton turned inside coming from the left wing. His low shot took a touch from Moore on its way in. Southport were in the lead and United didn’t look much like contesting the match from that moment apart from in the 81st minute.
A Luke Young free-kick curled over runners inside Southport’s box. Sean McGinty connected with the ball and sent it past Norman and into the far corner. The assistant referee raised his flag for offside.
A half-chance fell to Jamie Reid in added on time but Norman made the save.
United now have two weeks until travelling to Guiseley for their next National League match on November 12. United player-manager Kevin Nicholson expressed his disappointment at his team’s performance after the final whistle and a willing to get it right on the training pitch before taking on the Lions in Yorkshire.