Arsene Wenger conceded striker Olivier Giroud lost control in Arsenal's 2-1 Premier League win over QPR on Friday.
Giroud threatened to significantly alter proceedings at the Emirates Stadium when, with his side 1-0 ahead, he was sent off early in the second period for head-butting Nedum Onuoha.
Thankfully for Arsenal, Alexis Sanchez, who had scored the opener after missing an early penalty, turned provider for Tomas Rosicky to grab a second.
Charlie Austin pulled a goal back from the penalty spot, only for Arsenal to hang on and claim the spoils.
Speaking about Giroud's red card, which will earn him a three-match ban, Wenger told BT Sport: "It was deserved. He didn't control himself and that is, of course, a straight red.
"It completely changed the dynamic of the game. We were in control of the game and suddenly we are down to 10 men and only 1-0 up.
"It turned the game from comfortable to a mountain to climb. Olivier is a guy who stands up and admits mistakes. He knows he has made a mistake."
While Wenger was frustrated by Giroud's misdemeanour, the boss could do little but praise strike partner Alexis.
"He always gives you hope that he can deliver a chance," added the Frenchman. "Sometimes he has so much confidence that he is a bit too individual.
"But he is always efficient. He won the penalty, scored the goal and set one up."