Southampton 0-1 Manchester United

Romelu Lukaku scored his sixth Premier League goal of the season to give Manchester United a hard-fought victory at Southampton.

The result maintains United's unbeaten start to their league campaign, although they are second in the table, behind Manchester City on goal difference.

Their latest victory was not routine as Southampton piled on the pressure in the second half, and United's Marouane Fellaini had to clear Oriol Romeu's header off the line.

In a bizarre end to the match, referee Craig Pawson sent United boss Jose Mourinho to the stand.

Asked why he had been dismissed, Mourinho said: "I don't know. You have to ask the referee."

The Portuguese added he did not think he had gone on the pitch.

• Man Utd ask for CCTV over Lukaku chant
• Relive Southampton versus Manchester United as it happened
• Analysis and reaction from today's Premier League games

Saints give United a scare

After dominating the first half, it looked like being another routine afternoon for United.

But they had to defend deep after the break, with Southampton having the majority of the chances and possession.

United, who have only conceded two goals in six league games so far this season, ended the game with six defenders on the pitch as Mourinho brought on Chris Smalling and Daley Blind to hold on to the points.

Southampton had chances - Romeu's header beat David de Gea but Fellaini was well placed to clear it off the line, before the excellent Romeu shot narrowly wide from a tight angle.

Nathan Redmond also had a shot saved by De Gea, and not even the second-half introduction of forwards Manolo Gabbiadini and Charlie Austin could unsettle United's defence.

Southampton have scored only four league goals this season, but manager Mauricio Pellegrino can take huge encouragement from their second-half performance.

United do enough in first half

Southampton's dominance after the break was surprising, particularly given how the first half had progressed.

United attacked with a free-flowing nature that was pleasing on the eye. Their main successes came down the left, with Marcus Rashford's pace, technique and dribbling ability, along with his link-up play with Henrikh Mkhitaryan, causing the home defence problems.

And they got their reward when Lukaku scored in the sixth successive game for club and country, finishing from close range after Forster had parried his powerful header from Young's fine cross from the left.

Rashford then narrowly fired wide from a 25-yard free-kick but the visitors were forced back after the break and had to rely on counter-attacks.

They still had a couple of chances, Lukaku having an effort saved by Forster, and substitute Ander Herrera shooting over when well placed.

And they held on for a fifth win in six Premier League matches, with 17 goals scored and only two conceded.

Man of the match - Oriol Romeu (Southampton)

United's best start for six years - the stats

• Sixteen points from their opening six games is United's best start to a Premier League season since 2011-12.
• Saints have failed to score in eight of their past nine home Premier League games, with their 3-2 win against West Ham this season the exception.
• Lukaku has scored six goals in his six Premier League games this season - Louis Saha is the only other player to have scored as many goals in his first six games for United in the competition.
• Southampton have lost 11 Premier League games in 2017 - as many as they had lost in 2016, with 15 matches still to play this year.
• Mourinho's side have kept the most clean sheets (five) and conceded the joint-fewest goals (two) among the 20 Premier League sides this season.
• This was only the second time Southampton have outshot their opponents in a Premier League game this season (14-9), but they have failed to score both times (also vs Swansea).

'I was not expecting him match after match to score' - what they said

Southampton manager Mauricio Pellegrino said: "You have to score goals. We did well, we played a good game and it is difficult to control this team, but we have to learn and be more aggressive. We gave everything but one action changed the game.

"It is the most difficult thing in modern football to score.

"I think we controlled the game but we allowed them to play in counter-attack and that is something they are really good. They were under pressure all the time."

Manchester United manager Jose Mourinho said: "It is not always possible for high quality, but we fought hard. We did for 25 minutes what many teams do for 90 minutes - to have five at the back and defend.

"We had two chances to kill the game, which is what we felt we could do, but credit to them, they tried to play, they sent on a second striker to play more direct but we fought really hard and I am happy.

"The majority of our players did not play in the midweek match [against Burton in the Carabao Cup]. Maybe it was the heat because we don't see the sun in Manchester often. I felt the boys were not sharp, so the option was to go for the points.

"The way we attack is something we are doing since the start of the season, to defend like that was the first time that had happened to us this season.

On striker Romelu Lukaku, who scored his eighth goal for United in all competitions, Mourinho added: "I knew he would score goals, more for us than he did for Everton or West Brom, that is logical, but I was not expecting him match after match to put the ball in the net.

"He is a striker that is scoring goals, but his work is so important for us and he worked hard like everybody else."

What's next?

It is another busy week for United as they travel to Russia to play CSKA Moscow in the Champions League on Wednesday (19:45 BST), before returning to Premier League action on Saturday when they host bottom-of-the-table Crystal Palace (15:00 BST).

Southampton's next game is at Stoke City on Saturday, 30 September (15:00 BST).