Unfortunately, those players were never properly tested on a night when opponents only three places from the foot of League Two were reduced to 10 men by over-zealous refereeing seconds into what should have been their big night.
Ross Flitney, who was once Edwin van der Sar's understudy at Fulham, misjudged a harmless through ball, with the result that he grabbed it marginally outside his area.
There was no intention to gain an advantage, but the referee, Richard Beeby, produced a red card with an apologetic shrug.
As if that was not a daunting enough start to a venture into the unknown - Barnet had never met United in their history - Liam Miller extracted an even more disproportionate punishment with a curling free-kick just inside the post.
That went past the substitute goalkeeper, Scott Tynan. "I've not seen the playback, but I'd suggest a little bit of common sense at that stage of the match," said the Barnet manager, Paul Fairclough.
"There wasn't anything malicious. He wasn't trying to gain an advantage, so I thought it was a really cruel decision that ruined a lot of people's night. That made the game very difficult for us, but I was really proud of my players."
This was a United team which included only one player - Phil Bardsley - from the one which started against Spurs in the Premiership on Saturday.
There was Premiership quality, though, in much of Kieran Richardson's work, as befits a player with England caps.
He was not to be denied for long. After 19 minutes, United won another free-kick from a hard-pressed Barnet defence, this time on the right, and he swerved it through the ruck of players and inside the far post.
Giuseppe Rossi had two good chances to extend United's lead before half-time, but Adam Gross cleared his header off the line and Rossi then blazed over the top when Richardson had given him the opportunity to do far better.
Rossi made up for that miss six minutes into the second half when Lee Martin picked him out in the heart of the area with a precise low cross from the right. Rossi controlled the ball and swept it past Tynan in one clean movement.
Despite their early handicap, Barnet were never supine. Their prolific striker, Giuliano Grazioli, had put the ball in the net at 1-0, only to be denied by an offside flag and they finally got their reward 16 minutes from time when Dean Sinclair took advantage of Gerard Pique's stumble with a goal they deserved for battling against the odds.
There was still time for Sylvan Ebanks-Blake to capitalise on similar confusion at the other end for United's fourth.
Manchester United (4-4-2): Howard; Bardsley, Pique, Brown, Eckersley; Martin (Gibson, 75), Miller, Jones, Richardson; Ebanks-Blake, Rossi. Substitutes not used: Park, Smith, Silvestre, Steele (gk).
Barnet (4-5-1): Flitney; Hendon, Yakaba, King, Gross; Strevens, Soares (Tynan, gk, 2), Sinclair, Lee (Batt, 87), Bailey; Grazioli (Hatch, 75). Substitutes not used: Charles, Graham.
Referee: R Beeby (Northamptonshire).Reuse content