Marcus Rashford had been in the contest only two minutes when he sparked Manchester United’s third successive league victory.

On as a 68th-minute substitute, the 19-year-old initially won a corner when his cross was deflected out. Then from Henrikh Mkhitaryan’s delivery Rashford hit an instant finish beyond the Leicester City goalkeeper, Kasper Schmeichel, for his first goal of the season.

This followed Romelu Lukaku’s saved penalty just after the break and when fellow substitute Marouane Fellaini doubled the advantage eight minutes from time, United were heading for a two-point lead over Huddersfield Town and Manchester City at the top of the table.

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The performance had José Mourinho purring about his side’s resilience. “Normally when you miss a penalty with half an hour to go there is a little collapse,” the manager said. “We kept playing today.”

Despite having started the campaign with two 4-0 wins, Mourinho indicated that each player has to perform to retain their place as he dropped Rashford for Anthony Martial. With Craig Shakespeare opting for the same XI that beat Brighton & Hove Albion 2-0 last Saturday and lost 4-3 at Arsenal the week before that, both sides could be viewed as settled.

What Leicester hoped to do was stymie any early United pressure, having conceded here in the 22nd minute in last season’s corresponding fixture. Mourinho’s team went on to win that game 4-1 and here began by hitting Schmeichel’s area with crosses from Martial and Antonio Valencia. The response was a 20-yard Matty James sighter that David de Gea watched roll wide.

Of note during the early exchanges was Martial’s willingness to rove infield to take the ball and drive at the visitors. United were superior in possession, taking residence in Leicester’s half and moving the blue shirts expertly around. When Jamie Vardy threatened to break towards De Gea at speed, Eric Bailly’s assurance in killing the danger underlined United’s control.

Just before the 20-minute mark United appeared to have a fair goal scrubbed out. Lukaku swivelled and fired at Schmeichel. The Dane saved well but the ball rebounded to Juan Mata, who finished having pounced from a seemingly onside position but the assistant referee’s flag was raised.

After last year’s two trophies Old Trafford is a more vibrant arena. So it was that the noise ratcheted up when they next attacked. Lukaku threaded a clever pass to Martial along the left, he flipped a cross to the far post and Paul Pogba’s diving attempt went wide of Schmeichel’s right post. A breathless couple of minutes was completed when the keeper’s athleticism was again required to repel an effort from Mata.

Leicester offered flashes of quality in the rare openings they had. Shinji Okazaki’s sudden shot from 25 yards had to be monitored by De Gea but this was as close as the visitors were allowed to the Spaniard’s goal.

Most of the action was at the other end. Twice Pogba unloaded at Schmeichel from long range and Mourinho will have been pleased by how his midfielder bossed proceedings. He will be less happy with United’s inability to make their domination count. The sense was that a first strike might again herald a few goals for the home side, yet as half-time neared the game remained deadlocked as a 35-yard free-kick from Pogba smacked the wall and landed safely in Schmeichel’s hands.

Mourinho’s instruction for the second half might have been to be more ruthless. His team’s opening gambit was to pepper Schmeichel’s area again. Mata and Pogba aimed in crosses but both failed to find a team-mate. Martial was one of United’s better performers and it was his darting run that came close to prising Leicester open. He passed to Lukaku, who tried to turn but went down when tussling with Harry Maguire.

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Next Martial won the penalty from which Lukaku missed. The forward’s attempted delivery from the left hit Danny Simpson’s arm and Michael Oliver pointed at the spot. After Schmeichel debated the decision with the referee, Lukaku smacked the penalty to his right and the keeper made yet another fine save.

Moments later frustration for United nearly became despair when Riyad Mahrez bamboozled Phil Jones and skipped in along the right but De Gea saved his fierce drive. Next Mkhitaryan spurned a golden opening from Mata’s balletic twirl and pass. Instead of shooting straight away, his elaboration led to the chance vanishing.

When Shakespeare brought on Andy King and Demarai Gray for Okazaki and Marc Albrighton before the hour, Mourinho responded by bringing on Rashford for Mata in what proved a decisive move. Almost instantly came Rashford’s moment, as he was left unmarked to volley home. “Set pieces are our achilles heel at the moment,” Shakespeare said.

From here United closed the match down, Fellaini’s point-blank finish after some good work by Jesse Lingard – another replacement – sealing victory.

United have nine points, have scored 10 times and are yet to concede. It is an excellent beginning to their tilt at claiming a 21st title.

Mourinho: I am happy for Marouane, for Jesse, for Marcus

José Mourinho praised his substitutes after they were key in maintaining Manchester United’s 100% start to the season in the 2-0 win over Leicester. United head into the international break with nine points from their opening three matches and at the top of the Premier League. They have scored 10 times and are yet to concede.

After facing stiff resistance from the visitors and seeing Romelu Lukaka’s penalty saved Mourinho brought on Marcus Rashford, who put United ahead, and Marouane Fellaini, who scored shortly after coming on, having been set up by another substitute, Jesse Lingard, to seal United’s third victory in as many fixtures.

The 54-year-old refused to take credit for his substitutions but said: “This is about the quality of the players, the players are good, and not just good, they are motivated to help the players. It doesn’t matter if they play from the beginning, if they come from the bench. The group is solid, very, very friendly in between games and [there’s] great empathy. I’m really happy, not for me. When [managers] make changes, we always make the right changes, sometimes it works against us. I’m happy for them, for Marouane, for Jesse, for Marcus.”

Mourinho then turned to those critics who argue his tactics are overly defensive. “Maybe they are going to say that [I am defensive] because my team is not conceding goals,” he said. “Maybe they say I am defensive. We are playing well. Maybe in some matches we are going to be defensive and if the opponent is playing better than us we have to be pragmatic and defend but today we didn’t need that. I am not carried away, three matches, nine points is good, 10 goal difference is good.”

He added: “We are playing well. We didn’t have many matches last season where we played 90 minutes with the control we had today. Is [Jamie] Vardy a very dangerous player? I would say one of the most dangerous in the Premier League. Was he dangerous today? I would say no because we played very well to control that. Were Leicester very dangerous against Arsenal [in a 4-3 defeat]? Yes, I watched the match three times. Were they dangerous against us? No.”

Mourinho believes United’s work during the summer is key to the flying start. “We had a very good pre-season,” the manager said. “We worked really well. We had great conditions to work together, to be together in a beautiful atmosphere. We played against good teams, the best team in Europe [Real Madrid] twice. The pre-season was very complete and then we start the Premier League. We are playing well.” Jamie Jackson