Manchester United's travelling support ignored the requests to refrain from singing their chant about Romelu Lukaku which has been described as "offensive and discriminatory". The rules are simple: three points for a correct score, one for a correct result and none for an incorrect result.
Mourinho brought on Chris Smalling for Henrikh Mkhitaryan and then Daley Blind for Marcus Rashford, the first time United fans have seen notably defensive substitutions from their manager this season.
Dusan Tadic failed to prevent Ashley Young putting in a cross and neither Wesley Hoedt, who fell over, nor Ryan Bertrand could stop Lukaku getting his head to the ball.
Manchester United have won all three of their games in the 24-year-old's absence thus far against Everton, Burton Albion and Southampton, but the impending decision on what course of action to take regarding their record signing will nevertheless have the club and its fans on tenterhooks.
Mourinho says he does not understand the lyrics of songs during matches - with the exception of a simple vitriolic chant often aimed at him by opposition fans - but he praised the United contingent for helping his side to battle to a 1-0 win.
Manchester United coach Jose Mourinho was however sent off the technical bench just before final whistle.
"It's not always possible opera of high quality". It was a hard game but we fought really hard and I am really happy.
As we told you earlier today, United were sent on their way to victory by Romelu Lukaku's eighth goal in as many matches in only the 19th minute at St. Mary's and his strike remained the only goal of the game.
Saints striker Shane Long: "I thought we deserved more from the game".
Paul Pogba made an impressive start to the season for Manchester United before getting injured. "To limit them to one goal was a credit to our team but it was just a shame we couldn't get that equaliser at the other end".