Bernardo Silva gave City the lead midway through the first-half before Dino Mavropanos struck with a header minutes later.
“Football is unpredictable,” said Guardiola. “They have one chance and score one goal, but it’s happened in the past.
“Always this season we’ve had a team that’s controlled many aspects, but we were not able to score three or four.
“I remember Sunderland on the first of January; we play outstanding and created chances. Then after against Chelsea, then Brighton, and today.
“I’m not talking about Arsenal away where they deserved to win and against (Manchester) United when they were much better than us.
“But the other games we played we were much better. We have a lot of new players and maybe that’s why we aren’t consistent for 90 minutes, we have ups and downs.
“Games like Nottingham Forest define us a little bit because last minute Savinho shoots with no goalkeeper and no goal.
“It’s happened many times, we didn’t score enough goals. I accept it. Opponents can score goals, but we were always able to score a lot.
“This season it hasn’t happened. But I’m so proud of these players after a trip to Madrid, a tough result and then come to London and fight, fight, fight until the end.
“We played more controlled the first half and then in the second we had more dynamic players with Rayan, Tijjani, Phil, Jeremy that changed the rhythm, we did well but we could not win the game.
“Many things we have done could be better. Could be more aggressive in the first half with the last pass.
“In the end we need creativity with cross, shoot, dribbles but we have struggled with that a little this season. It’s not easy you know.
“I’m so respectful of both teams but they played with low blocks and on transitions. Madrid are more dangerous on transitions; Nuno is a master of set pieces.
“What can I say to the team? We have to be better in the final third and we didn’t do it, that’s all. It’s happened in many games this season.”