Mourinho could not afford any mistakes in this third-round tie after Premier League defeats by Manchester City and Watford, with a Europa League loss to Feyenoord sandwiched in between.
It was eventually smooth passage, assisted by Northampton keeper Adam Smith, who endured a nightmare evening and played a big part in two of United’s goals.
The highly rated 23-year-old picked up a back pass in the 17th minute and when Wayne Rooney’s resulting free-kick was blocked, the recalled Michael Carrick fired home the loose ball emphatically.
Alex Revell gave the Cobblers hope of a shock from the penalty spot just before half-time after Daley Blind fouled Sam Hoskins – but this was not the night for an upset.
United regrouped and Ander Herrera’s powerful drive put them in front after 68 minutes before Smith’s misery was complete seven minutes later when he missed a simple long clearance to allow substitute Marcus Rashford to roll the ball into an empty net.
Relive Wednesday’s EFL Cup action
Can Carrick unleash Pogba?
Jose Mourinho has been reluctant to use the 35-year-old England midfield man since his arrival at Old Trafford. This was his first start since Manchester United’s win against Leicester City in the Community Shield at Wembley.
On this evidence he surely has a strong case to force his way into Mourinho’s plans – not least because he possesses the style and composure to bring the best from United’s £89m world record signing Paul Pogba.
Pogba has looked restricted in his early performances and the selection of Carrick, so reliable in possession and even chipping in with a goal here, would allow the France midfield man freedom, play to his strengths and give him the opportunity to do damage further forward.
Carrick’s experience and expert reading of the game adds to Mourinho’s options and could finally bring the best from his showpiece summer signing. Surely he will start against Leicester City at Old Trafford on Saturday.
Rooney’s struggles continue
Wayne Rooney
Wayne Rooney has scored just once in six games for Manchester United this season
As Pogba got the night off and Zlatan Ibrahimovic and Rashford started on the bench with Mourinho making nine changes from United’s 3-1 loss to Watford at Vicarage Road, there was no respite for Rooney.
United’s embattled captain, who has bore the brunt of much of the criticism aimed at the side this season, was in the starting line-up but endured another night of frustration.
He worked hard but nothing is coming off for the 30-year-old. He missed one easy chance early on and when he did hit the target after Timothy Fosu-Mensah’s header hit the bar, he was adjudged offside.
With Carrick and Herrera excelling and with a host of attacking options available to Mourinho, will Rooney’s place come under threat against Leicester City at Old Trafford at the weekend?
Good night for Northampton?
Alex Revell
Alex Revell equalised from the penalty spot for Northampton
Northampton may not have been able to spring the big shock and increase the woes for Mourinho by knocking Manchester United out of the EFL Cup – but there was still plenty for the club lying 11th in League One to be pleased about.
The neat Sixfields stadium was packed with a record crowd of 7,798. With a new stand in the process of being built, the club can be proud of the way it handled the big occasion.
Northampton’s 31-game unbeaten run ended with defeat by Chesterfield on Saturday and for spells they showed United too much respect. This is, perhaps, understandable, but this was a night when Northampton as a club did itself great credit.
If there was a sadness, it was the disappointment suffered by keeper Smith, who has attracted Premier League attention but was badly at fault here.
Smith was included in the League Two team of the season as the Cobblers clinched the title in the previous campaign. There will be better days ahead for a talented young goalkeeper.
What they said
Manchester United manager Jose Mourinho: “It was as difficult as I was expecting but we looked to be in control for the first 35 minutes and then we looked to be in control for the last 45. I think the team was in control from the beginning and the subs were just a contribution.
“The game should be easier, we should have been playing against 10 men very early in the second half. Northampton fought and they tried to cause us problems which sometimes they did but it was a positive performance overall.
“I don’t like to individualise the players, I think it was fine, the midfield were in control.”
Northampton manager Rob Page: “When you get back in to it at 1-1 you never know.
“I’m really proud of the players, we had to be disciplined. They’ve had a tough week by their standards but we knew we had to be strong. When you give away soft goals you will get punished.
“He (goalkeeper Adam Smith) was outstanding last season and he’ll bounce back from this. He’s a strong character, we’ve all had moments like that as players.”