The Gunners were two goals down inside the opening 15 minutes, as Younes Kaboul and Troy Deeney scored for the visitors.
Alex Iwobi’s goal in the second half only reduced the deficit, as Arsenal are now in third place, nine points behind league leaders Chelsea.
“It was obvious we lost duels and were not sharp enough,” Wenger said in quotes reported by BBC Sport .
“It looked more mentally that we were not ready for the challenges. We were unlucky for the first goal which was deflected after a soft free-kick.
“It took us a while to get into the game, it was all us in the second half and we were unlucky not to get something from it.
“You look at the facts and we were beaten in the duels. When you play at home in our position, that is not normal. Everybody in the Premier League is strong physically and 90 per cent is not enough.
“We knew the solution was going wide, but we were not patient enough and wanted to give too many long balls. We did not pass the ball quickly enough and we have to stick to our game, then we are always dangerous.
“Where does it leave the league? We lost and we want to respond in the next game. You can only have a chance if you win your games. I knew exactly what we were preparing for, but we have to learn from it.”
Arsenal travel to face Chelsea on Saturday in their next league game.