McIlroy's side had enjoyed previous wins over Coca-Cola Championship sides Preston and Wolves in earning their third-round tie but found the test of facing the rampant Blades one step too far on Tuesday night.

McIlroy remained humble in defeat and conceded his side were beaten by a strong United outfit.

"They were class," he admitted.

"Every mistake we made was punished and their quality really shone through.

"The difference in class was too much for us to handle tonight, especially the finishing.

"They are still essentially a Premier League side, and the finishing of Billy Sharp was fantastic.

"Their movement, skill, everything - our boys learned a lesson tonight about giving the ball away."

McIlroy was quick to point out his side's shortcomings and acknowledged it was careless errors that handed the Blades their chances.

"You can't give it away in certain areas and we've done that tonight and conceded goals.

"I think there were 15 minutes there in the second half where we had a foothold on the game, but then we gave it away and it was 3-0, game over."

McIlroy even admitted he was glad Morecambe's cup adventure was over and attentions could be turned to League Two survival matters.

"Its been a great run for us and I'm glad we're now out of it," he said. "We've got bigger fish to fry now in staying in League Two and that's our main objective.

"This has been a great experience but let's get back to reality.

"We've earned this club some money.

"Now we can kick on - there's no use hiding or feeling sorry for ourselves.

"We were not disgraced tonight."

United went ahead after 18 minutes through clinical striker Sharp, who struck twice in quick succession. Sharp scored after being played in by Luton Shelton on the left-side of the area and slamming home powerfully into the roof.

He grabbed his second after picking up Derek Geary's lofted ball, turning his man and firing home.

Shelton got in on the act after beating the offside trap early in the second-half and slotting home, before the returning Lee Hendrie took advantage of a lapse in the Morecambe defence to drive in a fourth.

Fittingly, Shelton wrapped up proceedings with a deft effort which curled into the bottom-right corner, capping a dominant United performance which pleased their manager Bryan Robson.

Robson hailed the form of his two-goal strike pairing and admitted there were several positives to take from the victory.

"We were a little bit concerned before the game because we've got players coming back from injuries and squad players who haven't had many games so you put them up and think the performance could be a little bit rusty.

"Sammy came with his full team and tried to play football but our lads were magnificent.

"Our two forwards were outstanding today. Morecambe couldn't deal with Luton Shelton's pace.

"It was pleasing for me to see his understanding of link-up play really working tonight and he took into the game things we had been working on in training.

"As long as he continues to work, he could become a great player. We saw tonight skills he has got."

Aside from goal-scoring exploits, Robson was also delighted with other basic aspects of his side's play.

"I was pleased with our passing in midfield and our defending because we've been conceding too many goals.

"The clean sheet is very important for everybody's confidence.

"Within the club, we've got good forwards in good form, scoring goals. That gives me something of a selection problem, with which pairing to go on.

"The good thing about Billy is his link-up play and movement. It was good for him to get a couple, he could have realistically scored five."