Matt Ritchie’s strike after Jojo Shelvey’s free kick provided the lone score in the contest, with United’s defence again lacking.
Here, we rate the United players on their effort at St James Park.
David de Gea – Made a sprawling save from Jonjo Shelvey early on, but could do little about the goal. 7
Phil Jones – Typically threw himself around, put his body on the line and made some key interceptions, but lacked in composure at times. 6
Chris Smalling – Was lucky a tackle on the edge of the box on Dwight Gayle didn’t draw a foul as it could have easily resulted in a penalty. His booking for diving also set up the free-kick for Newcastle’s goal. 4
Antonio Valencia – Might have prevented the goal if he had drifted inside on the free-kick. Was later booked for a dangerous high kick. 6
Ashley Young – His delivery from set pieces left a lot to be desired and his defending at the back was far from ideal. 6
Paul Pogba – The midfielder was a ghost throughout, failing to make any sort of impact. Recognising that, Jose Mourinho replaced him immediately after United conceded. 5
Jesse Lingard – Had some decent link-ups with Alexis Sanchez and Romelu Lukaku, but nothing to write home about as his form has continued to slide. 6
Nemanja Matic – Sent a fantastic pass to Anthony Martial in the first half that the Frenchman should have scored from, but was overrun in midfield at times. 6
Alexis Sanchez – Appeared to be on the verge of breaking through on multiple occasions with weaving runs, but couldn’t pull a goal out of the bag. 7
Romelu Lukaku – Failed to find the back of the net again, but delivered some clever passes. He wasn’t the reason United drew a blank. 7
Anthony Martial – Wasted a clear opportunity after Matic dropped a sensational pass to him on the run, but credit also goes to Martin Dubravka for sending it away. Later had two chances from point-blank range and nailed the defenders in front of goal both times. 5
Juan Mata – Had little time to settle in but his passing was slick enough. 6
Michael Carrick – Not the type of player to bring on when you’re chasing and he couldn’t impose himself. 6
Hernandez and Arnautovic were both on target as the Hammers gave their survival hopes a major shot in the arm with a 2-0 win over Watford.
Mexico striker Hernandez headed his third goal in four Premier League games before half-time, and Austrian playmaker Arnautovic capped an all-action performance with the second 12 minutes from the end.
“Marko is an unbelievable, all-around player and it gives you a lot of confidence when you play up front with a player like him,” Hernandez told the club website.
“We have a good understanding with each other and both of us scored. That’s a good thing for a striker.
“Not only did we score, but the whole team ran with high intensity and we showed that we wanted the three points.
“Three points are three points whoever they come against, and we need to keep going day-by-day and game-by-game because every game is going to be a final.”
These two… pic.twitter.com/En2JVlQGr7
— West Ham United (@WestHamUtd) February 10, 2018
The duo now have seven goals apiece this season, with West Ham’s latest victory moving them up to 30 points, level with Watford.
Meanwhile, Hornets striker Stefano Okaka was not in their squad despite not being injured. Okaka had looked set to leave Vicarage Road before the transfer deadline with Fulham, Malaga and Galatasaray all linked, but a move did not materialise.
Yet he was not involved at the London Stadium despite boss Javi Gracia having only 17 senior players available.
“It’s another situation,” said Gracia. “This week he was out of training, he was out of the team. Maybe next week he will be with us, but at this moment I can’t say anything else.”
Aguero’s quadruple – incorporating his third hat-trick of the season – took his total for the campaign to 28 and his overall City tally to 197.
But as impressive as the Argentinian was, City again owed a lot to the irrepressible De Bruyne, who created his side’s opening three goals in another outstanding display.
“Luckily Kevin De Bruyne is playing for us and helping us to score,” said Aguero, who with 143 Premier League strikes is now only three short of moving into the competition’s top 10.
“I am very lucky because most of the goals come from his assists – I just have to hit the ball. I am happy for him as well. He is a great player and any team in the world would love to have him.”
Most of the pre-match headlines were made by Leicester winger Riyad Mahrez, who was back on the bench after ending more than a week of self-imposed exile following the collapse of a move to City.
But the Algerian could only watch as City raced out of the blocks.
The hosts took a third-minute lead through Sterling, the England international turning home a De Bruyne cross from close range to exorcise the memory of a miss from similar distance at Burnley the previous week.
The Foxes replied with a breakaway goal from Vardy but City took a grip as Aguero struck twice in quick succession after half-time. Leicester sent on Mahrez but to no avail, with Aguero netting twice more.
It was a good way to sign off from Premier League action for the month, with City having Champions League, FA Cup and Carabao Cup commitments in the next fortnight.
“The goals are very important because they help the team to win,” said Aguero. “But I think we are very close to achieving important things. That is why I am very happy, personally and for the team.”
Leicester boss Claude Puel, who insisted Mahrez had been welcomed back into the group, admitted his side were outplayed.
“They had more confidence, found more quality and took the space,” the Frenchman said. “We played against a good team and a fantastic striker in Sergio Aguero. He scored four fantastic goals.
“It is tough for us to concede five goals – it was a big disappointment – but we were a little lucky to come back in the first half and be on level terms.
“The second goal made it too difficult for us because they have the quality to play between our lines and recover the ball quickly, with strong pressing. It was too difficult for us to resist.”