The Scot had announced a week earlier that his 27th year in charge of the club would be his last prior to his side's trip to West Bromwich Albion 12 months ago today.
With a 20th (his 13th) English league title already sewn up, the pressure was off at The Hawthorns, which was bathed in Black Country sunshine as the curtain fell on another season.
Freed from any shackles of a title race, the champions dominated early on and by the 30th minute they had opened up a three-goal advantage. Shinji Kagawa nodded in from close range in the sixth minute, before Jonas Olsson put through his own goal. Full-back Alexander Buttner then added a third from a tight angle to seemingly end the game as a contest.
However, quickfire goals either side of the break from James Morrison and loanee centre-forward Romelu Lukaku reignited the home side's interest, although that it appeared to be on the wane again when one of Ferguson's last ever signings, Robin van Persie, turned in a cross from Antonio Valencia with 53 minutes played.
United's Mexican frontman Javier Hernandez added a fifth goal 10 minutes later, but once again the hosting Baggies refused to accept their fate.
Lukaku scored his second goal of the match nine minutes from time and then Youssouf Mulumbu cut the deficit to one during West Brom's very next attack. The comeback was then finalised in the 86th minute as substitute Lukaku completed his hat-trick following a goalmouth scramble.
The retiring Ferguson, perhaps emotionally exhausted after that rollercoaster encounter, declined the chance to take part in a post-match press conference, which left offers to pay tribute to him.
Goalscorer Hernandez said: "I can't remember playing in a match with 10 goals. We're a little bit frustrated because we wanted to win it for the gaffer and Scholesy (who also retired). The gaffer is certainly going to remember his last match in charge! He is going to remember this game. It's probably the first time United have been 5-2 ahead and not won.
"The gaffer has put the club on the top and we're going to miss him. I am going to thank Scholesy too. He's been an incredible team mate."
Meanwhile, Rio Ferdinand tweeted: "5-5.....what a mad result! Lets be honest the boss was never going out with a boring 0-0!!"
Michael Carrick, who captained United in Ferguson's last match in charge, offered: "It's a bit funny in the dressing room because of the situation. We've thanked the manager for everything he's done and he's thanked us. The manager wanted to win but with the job we've done this season, I'm sure he can retire very satisfied."
WEST BROM: Foster; Olsson, Ridgewell (Lukaku), McAuley, Jones; Yacob, Morrison (Fortune), Brunt, Dorrans, Mulumbu; Long (Rosenberg)
MAN UNITED: Lindegaard; Buttner, Jones, Evans (Ferdinand), Valencia; Carrick, Anderson, Cleverley (Giggs), Kagawa (Scholes); Hernandez, Van Persie