The enthusiastic applause from the home fans that followed initial disappointment, at the end of six minutes of injury time that did not bring the equaliser they craved, told its own story about Manchester United's performance.
They recorded 20 shots in a Premier League game against the Gunners for the first time since August 2011.
On that occasion, they scored eight times. This time, there was nothing.
Amorim spent most of last season grumbling about not taking opportunities. Yet this didn't seem like one of those days. Two-thirds of his new £200m strikeforce started the game - and Cunha, who is clearly going to be a crowd favourite because of the fight he shows in every moment, and Mbeumo were excellent.
Casemiro's passing range was superb. Patrick Dorgu was outstanding at left wing-back and Matthijs de Ligt a rock in central defence.
But they conceded far too easily.
It is easy to imagine United goalkeeping great Peter Schmeichel just barging William Saliba out of the way once Rice's pinpoint corner was heading under the crossbar. Edwin van der Sar was far too cute to be caught out so easily.
Bayindir ended up in a position from which he could have no influence. And Amorim, and Onana, who was at Old Trafford for the game, would only watch in despair.
In the brutal world of professional sport, results mask everything. Amorim has now lost 15 times in 28 Premier League games as United manager - that is the fastest a manager has reached 15 defeats in the competition, promoted clubs aside, since Paul Hart with Portsmouth in 2009.