Billy Sharp and Luton Shelton - United's new-look front pairing for the Carling Cup encounter with Morecambe - each grabbed a brace as Bryan Robson's side breezed into the fourth round.
The frontmen scored their first competitive goals for the club, as did Lee Hendrie, as United completed a hat-trick of wins against League Two opposition in the competition.
United will go down in the record books as the first team ever to defeat Morecambe in a League Cup tie. The Football League newcomers had already beaten Preston North End and Wolves to take their place in the third round.
Among the eight changes that manager Robson made for the Blades were Hendrie, back from a knee operation, and Geary, available again after a three-match suspension.
Despite a slow start, the Morecambe fans congregated on the Bramall Lane end, made themselves heard, whilst the early threats came from the pace of Shelton. Firstly, he won the encounter's opening corner and then turned Artell with ease, although United were unable to test the away team's goalkeeper.
Shelton was undoubtedly the star performer early on and it was his work, on 18 minutes, that brought United the lead. He beat two defenders on the edge of box and laid off for SHARP to fire past Lewis, who committed himself too early. It was the striker's first senior, competitive goal in a Blades shirt and he celebrated in front of the Valad Stand.
The goal helped the Blades relax and the home side looked more assured on the ball. On a rare assault, Morecambe thought they had levelled on the half hour, Stanley's volley from the edge of the box would have beaten most League Two goalkeepers but Kenny flung himself across his area to tip the ball around the post.
To rub salt into the wounds of the Morecambe fans, their deficit was doubled with United's next attack. With 33 minutes on the referee's watch, Geary delivered from the right and SHARP's excellent first touch enabled him to roll his marker and fire into the roof of the net. Goalkeeper Lewis, on this occasion, was given little chance.
Twice in the space of a minute Shelton looked to extend the lead further but his first effort was blocked and he scuffed the second - still in the same move - wide of the target.
Alan Quinn curled wide, whilst Naysmith cleared up a potential tricky situation when Twiss progressed down the left just before the half-time break.
Morecambe made a change at the interval and were the first to work an opening in the second half but Stanley's left-footer, after robbing Alan Quinn, was comfortable for Kenny.
United were quickly back on top and seven minutes into the half the lead was extended again. Stephen Quinn's ball through the defence saw SHELTON's pace beat the offside trap whilst his quick feet bemused Lewis before slotting into the empty net. It was a just reward for the impressive performance from the Jamaican.
Moments later Alan Quinn provided a cross from the right which Sharp just failed to connect with, whilst Morecambe hit back with a long-range drive from Baker which was just wide, although it forced Kenny into a full-length dive.
Lewis needed two attempts to gather a shot from Shelton, who came across from the right and then Sharp had a great chance to complete his hat-trick after being put through by Hendrie but the goalkeeper saved with his legs.
The fourth arrived midway through the second period and visiting boss McIlroy would have been concerned with the ease that United were getting through. From Alan Quinn's cross, Shelton failed to connect with a header and after the ball was half-cleared, HENDRIE took a calming touch before slotting into the bottom corner.
Seconds later Sharp was gifted another hat-trick chance but he again cannoned the ball against the goalkeeper's legs after being put through by Shelton.
Robson introduced a new central midfield pairing for the last 20 minutes but United's dominance continued and a fifth was added on 76 minutes. Stephen Quinn delivered into SHELTON who stepped inside his marker before also finding the bottom corner of Lewis' net.
Both sides completed their substitute allocation with the result not in doubt and Morecambe's best chance came in the final five minutes when Thompson cut in from the right and forced Kenny into another save, this time from a narrow angle.
Sharp was not destined to complete his hat-trick as Lewis clawed away a 90th minute header, following a Shelton cross, and the strike duo were afforded a standing ovation as they left the field.
Blades: Kenny, Naysmith, Shelton, Hendrie (Tonge 68), A. Quinn, Kilgallon, Montgomery (Armstrong 68), Lucketti, Sharp, Geary (Bromby 76), S. Quinn.
Unused: Morgan, Stead.
Morecambe: Lewis, Yates, Artell, Bentley, Stanley, Twiss, Baker (Hunter 76), Allen, Sorvel (Thompson 45), Blinkhorn, Adams (Grand 76).
Unused: Drench, Newby.
