Shots were few and far between for the remainder of the first half and after Rob Holding was forced off injured, five players picked up yellow cards for separate fouls in the space of 310 seconds. "That is clearly a team that is on a high, against a team that has so many problems", he said.
"They scored a second goal, if not it was not" [an open game], he said.
"We have to take all that into account and no matter what happens we have to try to get the three points". "As always we made mistakes and we paid for the mistakes", said United manager Jose Mourinho.
There is, however, a first league start for Diogo Dalot and returns in defence for Chris Smalling and Eric Bailly.
They did not drop their heads, but continued to press high and move the ball quickly, something we are not used to seeing from José Mourinho's United.More news: Alabama's Tua Tagovailoa facing ankle surgery
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"We make two big mistakes for their goals, other mistakes that allowed them to have counter-attack situations, easy passes that we lost, easy controls that we lost, and again our performance is marked a little bit by these ups and downs".
Aubameyang also saw a right-footed curler well parried away by De Gea and Arsenal remained the team in the ascendancy despite Mourinho having introduced both Romelu Lukaku and Paul Pogba. "Maybe we feel frustrated with the result, with some mistakes, some moments where a bit more quality was needed".
"I think Paul played well", said Mourinho.
"But we have to be happy with the spirit, the effort, the dynamic, the intensity, the understanding of our difficulties".
"Behind was a kid [Dalot] with a first start, Eric [Bailly] half-injured and without playing for a long time, Smalling injured - I have to say injured - Marcos Rojo's first minutes of the season, [Matteo] Darmian with a third start; it was lots of people in very hard circumstances". "I am happy with the soul and heart, but we are not consistent and uniform".
United were the better side after the break but they were struggling to pose much of a threat to Leno, with only a 30-yard strike from Rojo forcing the German stopper into any action.