The Italian coach felt the home side deserved to win on the strength of their second half display, but was upset with the nature of the defeat - handed to The Gunners by keeper Carlo Cudicini's awful mistake.
"How can I explain it?" he asked. "It was a bad goal. We conceded a bad goal. It is normal.
"The first half was good and tactical. The match was good for us in the first half, they scored a free kick, but did not have very clear chances to score in the first half.
"They put us under pressure in the second half and shot at goal too many times. We defended maybe too deep.
"I wanted to (make a) change. The referee was very close to me. He did not see us and they moved the free kick very quickly and scored the goal.
"I wanted to put Mario Stanic on the left flank to try and attack them from that position.
"He was ready to come on, he was there, so I said, after the corner, we make the change and the ball was close to us.
"The fourth official was even sure of the change but they started very quickly and the referee said okay.
"Who knows (if things would have been different)? It is another action, we have another position and they cannot surprise us."
Ranieri admitted he did not need to have too many words of consolation for Cudicini after his compatriot's mistake.
"Carlo has saved a lot of chances during his career," he added. "It can happen. It is done.
"We are used to him saving great shots but, today, he made a mistake. I said to him: 'Don't worry, look forward to the match'."
