Southampton ended Manchester United's 10-match unbeaten run and climbed above them into third place on English football's Premier League ladder thanks to a 1-nil victory at Old Trafford.
Southampton substitute Dusan Tadic scored the winning goal in the 69th minute to condemn United to defeat and deflate the optimism that had returned to the club's home ground.
Southampton, who snuffed out United with a textbook away display, have 39 points from 21 matches, while United drop to fourth on 37 points.
With just a point separating the two sides going into the match, the first half was short of thrills as Southampton restricted United's flow in midfield.
After a silky move Saints striker Graziano Pelle struck a shot against the base of the post and the ball rebounded to Tadic who kept his composure to fire past David De Gea.
United squandered a number of chances late on as Louis Van Gaal's side tasted defeat at home for the first time since the opening day of the season.
Earlier, Alexis Sanchez scored twice and created a third as Arsenal beat Stoke City 3-nil at the Emirates Stadium to move above Tottenham Hotspur into fifth spot with 36 points.