Ronald Koeman gave his side a simple message after defeat to Manchester United as he insisted “details make the difference.”

Koeman was frustrated to see his side boss their game against the Red Devils and yet come away with a third straight defeat that has knocked them down to fifth place in the Premier League.

The Dutchman was clearly annoyed about what happened during the 2-1 defeat at St Mary’s and said: “It’s always difficult before you are the better team and again you have to fight against the 1-2 down.

“After that moment we didn’t play well but that’s the difference.

“On this level, details makes the difference in football.

“The score is 1-2 and you can talk much longer about who deserved to win, who played football, who played offensive football, who did pressing, but everything is s**t because we lost.”

Koeman handed a second half debut to 18-year-old Jake Hesketh in a bid to try and get back into the game as injury hit Saints, for whom Toby Alderweireld failed a late fitness test, failed to take their chances and made two costly errors at the back.

Even United boss Louis van Gaal admitted that Saints were the better team and explained that he has to find a way to get his players producing the quality they offer in training on matchdays.

“In the second half, okay, we have not given a lot away but not so much in spite of that Southampton were the better team,” he said.

Before the game Van Gaal had said if they won this match they would have momentum but he conceded that given the manner of their win he could not be so bullish as to say that.

He added: "No, the performance was not good enough so I can not say it. I'm sorry, because we were the lucky team this evening but maybe because we are in the moment you can say that also."

The United boss also confirmed that the substitution of Paddy McNair before half-time was tactical due to the 19-year-old's lack of confidence.

"He had not any confidence so, he had already given three big chances away, and then I have to. It's very disappointing for me and also for Paddy, but I had to," he added.

"As a manager I'm responsible to win and after the change we played a little bit better."