Arsenal boss Arsene Wenger was unhappy with two key refereeing decisions in the 2-1 defeat at Manchester United.
The Gunners conceded a penalty when Santi Cazorla handled an Ashley Young cross and later had Jack Wilshere sent off for two rash challenges.
Wenger said: "We always have a penalty against us when we play Manchester United so we get used to it."
He also felt Wilshere did not deserve to be dismissed. "It looked harsh from the stand, the second yellow," he said.
Wilshere's second yellow was for what appeared to be a studs-first foul on Patrice Evra, and followed an earlier caution for a foul on Tom Cleverley.
He had been warned by referee Mike Dean for another foul prior to his second booking but Wenger decided not to substitute him.
"I considered taking him off but we had to go forward and attack. We were not in a position where we could defend and we didn't have a lot of midfield offensive options on the bench.
"I think we were a bit unlucky, especially with the penalty decision. We had the better chances but overall in a game like this you ought to not put yourself on the back foot when you are one down."
Wenger insisted he felt no extra pain at seeing former striker Robin van Persie score in the opening minutes against his former club.
He said: "It honestly doesn't bother me at all that Robin scored. You just want to win the game and you don't care who scores. What is most important is that you don't make mistakes at the back and give chances away.
"I'm disappointed because we had a lot of the ball but we were not very efficient. It was a bit of an illusionary domination. We gave an early goal away and in a game like that it is a massive advantage for a team.
"I think the start did not help us. It was important not to put ourselves in trouble, which is what we did. Then, when we were 2-0 down and down to 10 men, it became difficult. If it was 11 against 11 then we could have come back.
"We had a lot of the ball after we conceded the first, but they created more chances and deserved to win the game," admitted Wenger, who will aim to pick his side up for their Champions League group match at Schalke 04 on Tuesday.