Not the best performance from Leicester who on the whole struggled to break down a solid Sheffield United backline. However, enough to see them through.
In a game of not much quality, Riyad Mahrez left the field to a standing ovation from the Leicester faithful having provided the only moment of brilliance with his superb assist.
The Championship side ended the game with just the one shot on target as they failed to grow on their impressive start to the game.
A stronger than expected starting XI fielded by Claude Puel suggested that Leicester are taking the FA Cup seriously.
Sitting eighth in the Premier League, The Foxes sit in a healthy position allowing them to put their focus on the cup.
Vardy to the rescue
Jamie Vardy opened the scoring as his header looped over a helpless Jamal Blackman.
Just over an hour into the game and the Mahrez-Vardy partnership shone through as the two combined for the goal.
Mahrez provided an incredible cross that found Vardy at the far post and he broke the deadlock with a fine finish.
Having missed two great opportunities in the first half it seemed certain that Vardy would not miss a third and he more than made up for his missed chances with the looping header.
Lacking quality in final third
It was a fairly dull start at the King Power Stadium. The hosts struggled to retain the ball as the Blades enjoyed the lion's share of possession.
Jamie Vardy had the first real chance of the game after his curling shot flew just a whisker wide of the far post.
Shortly after, Leicester grew into the game as they enjoyed more of the possession and began to test Jamal Blackman more frequently.
Leicester quickly began to dominate the game as Vicente Iborra came inches away from opening the scoring after a superb cross from Riyad Mahrez.
Despite a positive start by the Blades, they quickly began to lose possession at an alarming rate allowing Leicester to break.
Harry Maguire came to the rescue for the home side against his former club as he blocked Enda Stevens' shot from close range, a certain goal denied.
Vardy should have opened the scoring half an hour into the game. Mahrez slid the Englishman in but Blackman pulled off a fine save to keep the proceedings level.
The Jamie Vardy goal certainly changed the game in the favour of Leicester, following the goal the home side looked much more dangerous going forward.
A new lease of confidence looked instilled in the Foxes and just minutes later Vardy had the ball in the back of the net again.
However, the goal was disallowed as Mahrez who had headered the ball down to Vardy was ruled offside in the process.
Blades boss Chris Wilder was forced into making a double substitution as his side looked for an instant response.
The inclusion of Ched Evans and Mark Duffy showed United's intent of pulling a goal back but Leicester continued to dominate the possession.
Job done in the end
Although Leicester created the better of the chances, their 4-4-2 formation looked to hinder their dynamic attack.
Kelechi Iheanacho played up top with Vardy but the two never seemed to show any signs of linking up.
Mahrez looked to be the Foxes most positive outlet as he cut inside with his usual tricks but he did not appear to have a passing option in Iheanacho.
Although United's back line looked more difficult to break down in the second 45, there appeared to be a total lack of efficiency from the hosts' attack.
Leicester enjoyed the large majority of possession yet when in the final third they really struggled to find the final pass needed to break through on goal.
However, the hosts got the job done and now await the draw ahead of the quarter-finals.