A brace apiece from Wayne Rooney and Juan Mata earned the reigning Premier League champions all three points and ensured that a new era at the Theatre of Dreams got off to the best possible start.
United were far from their best in the opening exchanges, but at the end of a hectic week the final result was all that mattered.
Rooney ensured that would be favourable as he stroked home his first from the penalty spot after Danny Welbeck had been bundled over in the box by Steven Whittaker.
The opener arrived four minutes before half-time, and three minutes after the interval Rooney had doubled United's lead as he slipped on the edge of the area but saw a skidding drive nestle in the bottom corner.
Damage limitation quickly became the name of the game for Norwich, but they were breached on two further occasions in the space of 10 minutes just past the hour mark.
Mata, within three minutes of being introduced, turned home a Phil Jones cross from close range to end the game as a contest, and it was to be the Spaniard who added a fourth as he glanced in a volleyed centre from Antonio Valencia.
The 'Chosen One' banner had gone, David Moyes' big summer signing Marouane Fellaini was not even on the bench, and United fans sang the name of their new manager throughout.
Giggs was hailed like a Hollywood star by the home crowd - many of whom will want the Welshman to take the job ahead of Louis van Gaal, who is the front runner to replace Moyes.
The United fans yelled "Attack, attack, attack" immediately after the first whistle, but the players failed to respond initially.
What was happening on the pitch was something of a sideshow. All the focus was on Giggs, who was the subject of several supportive chants from the stands.
When Giggs came off his bench into his technical area for the first time after six minutes, he received the kind of applause especially reserved for club greats.
United's record-appearance maker and most decorated player had come to the edge of his box to urge his players to up their game.
In truth, for the first 10 minutes there was little difference from the Moyes era.
Just after Norwich had a Jonny Howson goal ruled out for a foul in the build-up, United had their first chance when Welbeck slammed a powerful half-volley at John Ruddy, who punched the ball away.
The tempo increased just before the break. Shinji Kagawa turned home Phil Jones' cross, but it was ruled out for offside. Valencia then belted a low ball at John Ruddy, which he saved.
The increased pressure resulted in United winning a penalty. Whittaker pulled Welbeck back and Rooney drove a low shot past Ruddy.
Less than three minutes after the restart, United were 2-0 up thanks to some inept defending from Norwich.
Four defenders failed to come out to challenge Rooney, who, despite slipping, curled a right-footed shot past Ruddy and into the net off the far post.
Sir Alex Ferguson and many more United fans got to their feet to clap Welbeck off on the hour as he was replaced by Mata.
Three minutes later Mata found the net as he turned home Jones' cross from close-range.
Soon after Mata had his second after he nodded home Valencia's centre from close range.
Substitute Javier Hernandez should have made it 5-0 late on, but fired wide went sent clean through.
Martin Olsson's deflected shot looped towards goal in injury time, but the ball hit the bar instead. Nothing, it seems, was going to spoil Giggs' special day.