The first half was dominated by Southampton but the home side failed to create any clear-cut chances. They were made to pay five minutes before the break, when Fletcher converted his first opportunity of the match. Stephane Sessegnon's shot was mis-hit and fell to the Scottish striker, who converted in a fashion which has become customary this season.
The second half was just as frustrating, Sunderland nullifying any threat from the home team, who were particularly disappointing with their set-piece and crossing delivery. Time after time the first man was hit.
Southampton did create occasional chances in the last 10 minutes, but could not break down a resolute defence that gave the visitors only their second away league win since February.
The game pitched together the two sides directly above the relegation zone, and was billed pre-match as a relegation six-pointer. Nigel Adkins had Adam Lallana out with a knee injury, whilst his opposite number Martin O'Neill welcomed Danny Rose back after a lay-off.
Sunderland almost took the lead after less than thirty seconds, with a Sessegnon shot fabulously tipped wide by Kelvin Davis, but Southampton were soon into their stride. Lambert had a free-kick deflected just wide and Gaston Ramirez tried on multiple occasions from outside the box, but there were no clear-cut chances.
With the game meandering towards the break, Sunderland scored against the run of play. A ball was played to Sessegnon in the area, and the forward scuffed a shot straight to the feet of Fletcher. Fletcher had been holding his back throughout the first period, but finished beautifully past the helpless Davis from fifteen yards.
Southampton made early changes during the second half, but they struggled to find their rhythm as the crowd began to groan at the lack of quality from both teams. Jose Fonte had a header cleared from near the line, but the Saints struggled to get support for Rickie Lambert up front.
The home side's set-piece delivery was particularly disappointing, and opportunities to threaten were consistently wasted by hitting the first man. The game reached the last fifteen minutes without Simon Mignolet being tested sufficiently.
Southampton did have occasional late chances, but Sunderland defended immensely in order to hold out for a well-earned victory, and the 2,000 travelling supporters were rewarded for their 300-mile journey.