Jose Mourinho's Manchester United maintained their strong start to the season after grinding out a 1-0 win away to Southampton on Saturday afternoon.Romelu Lukaku's 20th-minute strike was enough to earn all three points for United at St Mary's and also helped the 24-year-old Belgian to equal a club record.The man who moved to Old Trafford from Everton this summer joined Louis Saha as the only other player to score six goals in his first six Premier League games for Man Utd.

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United looked very good in the first-half, especially on the counter attack, but they failed to kill off the game and Southampton pretty much dominated proceedings in the entire second period.

Mourinho admitted that the match against the Saints was his United's toughest encounter of the campaign so far, and he has an interesting explanation for his side's below-par performance.

Mourinho on Man Utd 1-0 Southampton

In a post-match interview, Mourinho told the BBC: "I'm happy that we coped with something new for us in this season, which was to play a defensive game in the last 20-25 minutes.

"We try to be positive. We try to score goals and to control matches. It's not always possible. The (Man United) players, they knew that since the beginning of the season."

The "Special One", who was harshly sent to the stands late on by referee Craig Pawson after running onto the pitch, continued: "They knew that the difficult time would arrive, and the difficult time arrived today.

"In the last 20 minutes, they (Southampton) played with two strikers, they played direct, they projected (their) full-backs, they had a go at us. And then, we defended, and we did what almost everybody else is doing in the Premier League, which is to play with five at the back."

What is Mourinho blaming for below-par display?

With Southampton putting on the pressure, Mourinho took off Juan Mata for the more defensive-minded Ander Herrera before bringing on defenders Daley Blind and Chris Smalling.

The Mail on Sunday's chief sports writer Oliver Holt has revealed that the Man Utd boss believes his team's poor display was down to the sun.

No, we're not joking, and as you can see in Holt's tweet below, when some reporters laughed at what he said, Mourinho replied by saying: "Seriously."

The sunny weather may have been a factor in what was United's hardest game so far this term, but it's always a good sign when you pick up maximum points without being at your best.

Eric Bailly and Phil Jones impressed yet again, David de Gea kept another clean sheet, and United showed that they don't have to score shedloads of goals to win games.

United fans will be well aware that this was the type of match they probably would have drawn last season - and in fact, the corresponding fixture in 2016-17 ended 0-0.

The Red Devils now turn their attention to Wednesday's trip to Russia in the Champions League to face CSKA Moscow before hosting struggling Crystal Palace in the league.

What did YOU make of Man Utd's performance in the win at Southampton? How important was it that their defence saw out the 1-0 result? Have YOUR say in the comments box below!