Arsenal manager Arsene Wenger admitted he was frustrated after his side were beaten 1-0 by Manchester City in the Carling Cup quarter-final at the Emirates Stadium.
The hosts created several chances throughout the 90 minutes while City's only effort on target proved to be decisive, as Sergio Aguero converted with only seven minutes remaining.
Korea striker Park Ju-young and winger Alex Oxlade-Chamberlain forced fantastic saves from goalkeeper Costel Pantilimon in the first half, whereas Lukasz Fabianski remained untested.
Wenger labelled his much-changed side naive after they conceded late on, Aguero's goal stemming from an Arsenal corner.
He said: “It was an unfair result but I felt we were a bit naive.
“I felt as well we did not take our corners very well but overall what is frustrating is that we lost a game we looked the winner of.
“We put a lot of effort in and are not rewarded. We lacked a little bit of experience to be decisive in the final third.”
Wenger did take some positives out of the game but insisted the Premier League was always his priority despite being so close to the semi-finals of this competition.
“I think in midfield (Emmanuel) Frimpong did well and (Francis) Coquelin did well,” he said. “Sometimes you could feel in the final third we lacked a little in creativity — but overall we did well and I cannot fault the team. They did very well and showed heart, quality and desire.
“You can argue that we lost the easiest trophy to win, but if you look at the teams who are still in it doesn't seem as easy to win as usually.
“I consider the championship the most important for us, more than anything else it is important to finish in the top four.”
City boss Roberto Mancini was happy with the result, the club's first victory at Arsenal in 28 attempts.
“We had a chance seven minutes from the end and we scored. It was a great goal. A great counter-attack,” he said.
“I don't think that Arsenal had a lot of chances, I think we played well. It will be better to win here in the Premier League but it is a good feeling because we are into the semi-finals of the competition.
“We have a strong squad — all of the top teams have a good squad and can change eight, nine or 10 players. It is normal for the Carling Cup to change.
“December and January will be crucial months because we play tough games and we play every three days. After January we can talk about whether we can win things or not.”
Mancini included former Arsenal midfielder Samir Nasri in his starting line-up, with the France international being jeered ferociously throughout the game before reportedly being involved in a post-match spat with Frimpong.
The reception from the home support was something which Mancini believes may have affected Nasri's performance.
“He can play better because he is a top player,” he said.
“Tonight is the first night he came back to Arsenal and it is not easy for a player that played here for four or five years.
“I think that he can improve a lot but it was the same situation with those who arrived last year, like Edin (Dzeko) and David (Silva).
“It (the win) is not important for him, it is important for the team. For him it is better than he played tonight so when he comes back to play here in the league he knows what will happen.”
Adam Johnson’s delightful flick laid on the only goal for Agueroand the winger said the victory showed the team have the heart for a battle.
“It was a tough game, it's been a long week and a lot of travelling, but we've come away with the win and we're through to the semi-final. We changed the team around, it was the second-stringers if you like, but we're progressing as a team and as a club and I hope it continues.”
That progress has seen Johnson play only a fringe role for much of this season, but he said: “For me and the lads who are playing in this competition, it's a chance to try and get in the team week in, week out. And if we can get into the final and win another trophy, it's important for the club.”
Striker Edin Dzeko, who was also involved in the goal added: “We played like a team, that's most important. I am trying to do my best every game and I think today was okay.”