Arsenal had looked in control of the clash after Alex Iwobi put the north Londoners ahead early on.
Hatem Ben Arfa trolled Arsenal boss Unai Emery (Image: GETTY)
However, Sokratis Papastathopoulos was sent packing before half-time for a second booking.
“The red card changed the game more than we wanted,” Emery said.
“The first 40 minutes we controlled, we scored, we didn't concede good chances.
“But after this red card it's different, more than we wanted. I think we can do better.
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Sokratis Papastathopoulos was sent off last night (Image: GETTY)
“The result for the first 90 minutes is hard for us but we are going to start the next match next week with 11 vs 11 and with the same respect we had in the first half. The first 40 minutes, we are going to do that at home.”
Emery appeared visibly irritated with Sokratis after the Greek international was given his matching orders.
The experienced chief played down any drama with the centre-back though.
He added: “A red card can come. It was the referee's decision.
Alex Iwobi had put Arsenal in front (Image: GETTY)
“I cannot speak to Sokratis, he has very good commitment and behaviour. He received two yellow cards for actions in playing.
“We are going to think for next week. We are going to start 11 vs 11, without Sokratis, without Lacazette. We have players.
“We can come back. The result is not good. It's bad.
“This is going to be tough. We need to play with the focus.”