Alex Iwobi scored an away goal just three minutes into the game. But Rennes equalised immediately after Sokratis was given his marching orders for a second yellow card shortly before half-time, with the Ligue 1 side eventually prevailing 3-1 after two second half strikes.
"Yes, [the red card changed things] more than we wanted," Emery explained to the media at his post-match press conference, via Arsenal.com.
"The first 40 minutes I think we controlled, we scored and we didn't concede good chances to them. But after this red card, it's different. It's more than we wanted and I think we can do better."
The Spanish coach, who won the Europa League three times with Sevilla, acknowledged the size of the task now facing Arsenal to overturn the aggregate deficit, but will ask his players to repeat the first 40 minutes of this game in the return leg next week.
"The result is for the first match and for the first 90 minutes. 3-1 is hard for us, but we are going to start the next match, next week with 11 against 11 and with the same respect we have had in the first half, the first 40 minutes," he commented.
"We are going to do that at home against them. But we need to also change our performance and I have the confidence with our players, with our supporters helping us to create one big atmosphere to give us a good spirit against them to comeback."
Emery appeared to have few qualms over whether Sokratis deserved his dismissal, diplomatically stating, "...a red card can come. Two yellow cards and it's the referee's decision."
He also has little concern that it was the third Arsenal red card in the space of three games after Alexandre Lacazette was sent off against BATE Borisov last week and Lucas Torreira saw red in the north London derby against Tottenham at the weekend.
"I think it's not easy. We can analyse these three red cards individually," he said.
Source : 90min