The chastening defeat at Leicester in Van Gaal's sixth game as boss was remarkable for the meek manner in which a United side capitulated.
Back when Jamie Vardy was a small-time part-time hardman, United lost their nerve - and heads - against the newly promoted outfit with an expensively assembled attacking quartet of Wayne Rooney, Angel Di Maria, Robin van Persie and Radamel Falcao.
United never played so expansively again after that defeat: Van Gaal was striving for balance but over the next 15 months the emphasis was, largely, on defence and forward after forward toiled in his team.
However infuriating United's reverse at the King Power was, they entertained more than they ever did in victory this term.
Muddled thinking against Arsenal
With Chelsea and City eliminated in the fourth round, United had a terrific chance to end their FA Cup drought, staggering through to the quarter-finals where Arsenal awaited at OT.
The Gunners had not won at United since 2006 and, still managed by the one-dimensional tactician Arsene Wenger, Van Gaal held the upper hand.
Then he decided to start Daley Blind in midfield.
Wenger's fleet-footed aesthetes rang rings around Blind and the isolated Marouane Fellaini, yet United went in at half-time level.
Van Gaal had needlessly started the unfit Luke Shaw and withdrew him at the break, also taking off Ander Herrera instead of the blowing Blind as Arsenal went on to win comfortably.
Van Gaal was the architect of his own downfall and had just let slip his best chance of silverware.
United enjoying a sprightly sping as we blitzed Tottenham, bossed Liverpool and battered City in a six-game winning Premier League run in an innovative 4-3-3 formation.
Across the pond in pre-season, United were set up in a rigid system with two holding midfielders and the winger Memphis starting as a playmaker.
Despite the drudgery this season, Van Gaal has loyally retained the formation and as a consequence we've played more tediously that we ever did under Moyes.
Failure to replace Rooney
Van Gaal gave Rooney the benefit of considerable doubt when he began the season with the United captain as the squad's only recognised striker- effectively disregarding James Wilson.
Rooney has suffered a steady decline since 2012 and Sir Alex Ferguson knew as much when he left it to Moyes to dot the i's and cross the t's on his sale.
Instead United gifted in indulged Rooney so much that he became undroppable.
Even when United belatedly signed a striker in the raw Anthony Martial (what a waste of money), Van Gaal could not bring himself to demote Rooney.
The Reds struggled for goals and form inevitably deteriorated.
Rooney was more effective in the second half of the season and Marcus Rashford emerged, yet United still only scored just one more goal than fourth from bottom Sunderland.