Paul Scholes - 20 last November - and 19-year-olds Keith Gillespie, Nicky Butt and Gary Neville all appeared, as thirtysomethings Mark Hughes and Brian McClair were rested.
"I felt I needed to freshen things up," Ferguson said. "Hughes and McClair had played three games in five days. The youngsters now realise what playing for United really means. That was the best part of the game for me.
"They are put on a pedestal, but people forget they are still young boys. Ryan Giggs is still only 21, and the others are 19 and just starting out.
"The important thing is they always want to try things even if they make mistakes. But they also did some fantastic things which need temperament and bottle. It will do them good to hear the crowd groan at a mistake. The crowd were not overkind to them, although they have always been good to young players here.
"It will have done them a lot of good - they made mistakes, but that is part of growing up. The more I can give the younger players the experience they had against Coventry, the more it will help me in the long run."
Scholes captured the headlines by pouncing for the first goal, which had Ferguson comparing him to Denis Law, and creating the second for Eric Cantona to stroke home a penalty.
Scholes has now struck six goals in six starts this season, and could be the answer to Ferguson's need for more English strikers, with the Welsh international Hughes's future at Old Trafford still to be decided.
United's victory - their first at home for three games - kept Blackburn firmly in their sights, with the match between the top two at Old Trafford just over two weeks away. United face a testing FA Cup trip to Sheffield United and a journey to Newcastle before Blackburn's visit.
Peter Schmeichel, United's goalkeeper, is hopeful of a return soon after missing the last nine games with a back injury, while Paul Ince could have recovered from a hamstring strain.
Mick McCarthy, the Millwall manager, fears Arsenal could hit his team on the rebound in Saturday's FA Cup match at the New Den.
Off-field controversy and poor results have contributed to a deepening crisis at Highbury, but McCarthy feels that may be bad news for Millwall.
"It concerns me that Arsenal haven't played well in the last few games," said McCarthy. "It's well known that when they are struggling they come back and play at their peak. I saw them beaten by Queen's Park Rangers when they were very poor, and I am su r e they cannot play as badly as that again."
Millwall appear to have run out of steam after a sequence of six successive wins. They followed Sunday's draw with Charlton by sharing the points with Oldham on Tuesday.
Oldham took the lead with Lee Richardson's penalty after Ben Thatcher toppled Oldham's player/manager, Graeme Sharp.
Alex Rae equalised from the spot with his seventh goal of the season after Nick Henry tripped Mark Kennedy, but Millwall felt they should have had a second spot-kick when Richard Cadette tumbled under a challenge by Steve Redmond.
Sharp was unhappy about the award of the Millwall penalty, accusing Kennedy of faking. "I didn't think it was a penalty and the lads all thought the boy dived," he said, "but the referee was itching to do something like that after giving us the first penalty."