First-half goals from Daniel Jebbison and Jayden Bogle booked the Blades' place in the next round in the first half at The Den, ahead of the league meeting between these two sides next month. The Lions, normally so dangerous on their own patch, were limited to essentially one shot on target with back-up goalkeeper Adam Davies keeping a clean sheet after being handed a rare start in place of Wes Foderingham as one of six changes. United player ratings: Ndiaye and Jebbison catch eye in Millwall victory And Rowett admitted: "We didn't play with anywhere near the quality we needed. You concede two poor goals against a team like Sheffield United, and you'll give yourself a mountain to climb because they have some good players and move the ball well. "We had a couple of good chances and a couple of good half-chances. We had moments to make the game interesting but frankly the performance didn't deserve to do that. We were poor and I'm disappointed. "We played well in the last game and didn't play well in this one. We weren't proactive enough and a little bit static in possession at times. They're a good side, but you can't get done with that movement and balls in behind. "We just didn't get going and the performance level wasn't anywhere near good enough to beat Sheffield United."