City were beaten 3-1 on the night — 6-6 on aggregate — ensuring Guardiola failed to reach the semifinals of the competition for the first in his managerial career.
The Spaniard had predicted two attacking sides would go head-to-head, but City failed to have a single shot on or off target in the first half as they trailed 2-0 at the break.
His side improved massively in the second half and retook the advantage in the tie with Leroy Sane’s 71st minute goal, but Tiemoue Bakayoko’s header six minutes later meant City crashed out.
Guardiola believed the game was lost in their tame first half performance while they could have scored more in the second, with Sergio Aguero and Sane spurning good opportunities.
“No, it’s not about the defence. Today was not about that,” Guardiola told a news conference. “Why was the second half a problem with the defence?
“The problem was the first half when we were not there. Our strikers have to be aggressive and pick the ball up, but we didn’t. At this crucial time. That’s why we are out.
“We have to play more than 45 minutes. It’s not about the defence and the goalkeeper. In the second half we won the second balls and how many chances did they create? Nothing.
“The gap between our first and second half performances was too big. It will help us a lot in the future and learn from that. That is my feeling now.”
But Guardiola insists he isn’t about to changing his tactics despite City being overwhelmed at times during the first half as Monaco’s swarmed over his players and stopped them from playing.
“I came here to win the Champions League? Ah. I tried. I tried. And I will try again,” he said. “Playing like we have done this season, like in the second half, would have been enough.”
As poor as City were in the first, Monaco were exceptional with Bernardo Silva running midfield and striker Kylian Mbappe causing constant problems.
Guardiola congratulated the Ligue 1 leaders on their victory but refused to predict how far they could go in the tournament.
“All the people expect their team to win the Champions League. The English media think City should win the Champions League, the French think Monaco can,” he added.
“There are a lot of good teams and we have to accept that, next season, we need to do better to try and get into the next stage.”
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