Manchester United 0 Southampton 1
Ronald Koeman gained revenge on his old adversary Louis van Gaal as Southampton recorded their first win at Manchester United for 27 years.
Second-half substitute Dusan Tadic stroked the ball calmly past David de Gea in the 69th minute to give Saints a 1-0 result at Old Trafford.
A near full-strength United, who started with Angel di Maria up front, were poor all afternoon and rarely looked like beating Fraser Forster in the away goal.
Their case was not helped when Robin van Persie hobbled off with an injury in the second half.
Saints Jose Fonte said: “It’s not every day you get a win at Old Trafford against a great team so for us it’s a pleasure and something we should be proud of.
“There’s a long way to go but it’s another three points. We got a lot of confidence from this game.
“It was a game that we defended really well, and they only had shots from outside the box if I’m not wrong.
“It was a fantastic game this afternoon.”