It took 70 minutes for José Mourinho's side to make the breakthrough, as substitute Marcus Rashford smashed home from a Henrikh Mkhitaryan corner.
Substitutes Jesse Lingard and Marouane Fellaini combined for the second and ensured the Red Devils kept up their perfect start to the Premier League season.
David de Gea - 7: Such was the dominance of the home side, De Gea was again rendered little more than an interested spectator at the Theatre of Dreams. He denied Riyad Mahrez on occasion and produced a simply world-class close-range stop to deny Andy King in second-half stoppage time.
Antonio Valencia - 7: In a game of constant United attacks, Valencia's position on the pitch would've resembled that of a right winger. The skipper was a constant attacking threat for the league leaders, and made sure that Marc Albrighton and Demarai Gray were no source of danger on the counter-attack.
Phil Jones - 8: The England centre-back is enjoying a career resurgence at Old Trafford this season. A third successive solid performance at the heart of a relatively untroubled United defence puts Jones in a good position to be first-choice all year long. The way he marshalled Jamie Vardy was impressive all afternoon.
Eric Bailly - 8: Similarly to Jones, the Ivorian has enjoyed a very comfortable start to the season. His sheer physicality and good positional awareness has nullified opposition attacks, with a solid barrier in Nemanja Matić in front of him.
Daley Blind - 6: It was an interesting game for Blind, as he obviously endeavoured to attack when the Red Devils were dominant, ably assisting the likes of Rashford and Juan Mata when going forward. However, he was caught out of position a few times by Mahrez, and the Dutchman will have to balance his game when facing bigger attacking threats in the future
Nemanja Matić - 8: Any questions over Matić joining the Red Devils have been well and truly answered already. The break-up play he's displayed in his opening three games has been exceptional, and the ability to transition into attack is what sets the Serbian apart.
Paul Pogba - 8: The Frenchman has started the season in fine fettle, and continued his good form against the Foxes. Pogba was popping up in acres of space in the first-half, and dictated the play as United searched for an opening goal. While his performance waned in the second-half, he was still at the heart of the play and instrumental to Mourinho's side.
Juan Mata - 7: The little Spaniard endured a frustrating day at Old Trafford. He was neat and tidy as always, playing intricate passes and always moving around, but nothing ever resulted of it due to the stern Leicester defence. He did put the ball in the net in the first-half, only for it to be disallowed for offside.
Henrikh Mkhitaryan: 7: It might've taken a year, but the Armenian is now looking like the player that was signed from Borussia Dortmund. Five assists in three games perfectly illustrates the influence he is having on this Manchester United team, grabbing another here with his corner for Rashford's opener.
Anthony Martial - 7: The French winger got his well-deserved start after sparkling contributions off the bench thus far, and although he couldn't add to his goal tally, he terrorised Danny Simpson all afternoon. The penetrative running was a constant, and he was a nightmare for the whole defence until he was substituted late on.
Romelu Lukaku - 7: Similarly to Martial, despite being unable to keep up his impressive goal record, the big Belgian influenced the game for his side. His hold-up play improved significantly as he tussled with Wes Morgan and Harry Maguire, and his ability to link up with the forwards around him made his presence vital for United. Lukaku's penalty was well struck but ultimately well saved by Kasper Schmeichel.
Marcus Rashford - 9: The whole game changed when Rashford was brought on, pace down both wings was just too much for Craig Shakespeare's side to deal with, and he took his goal wonderfully well, which was very much deserved after an unfortuante start to the season.
Marouane Fellaini - 8: United's midfield this year couldn't be more physically imposing. Fellaini is key in that, as his performance from the bench displayed. A rather lucky strike from the Belgian secured all three points.
Jesse Lingard - 8: Another of United's substitutes who had a big influence, Lingard's dynamic run was the catalyst for the second goal, as his shot found the back of the net, deflecting off Fellaini's knee.