Glasgow: Manchester City manager Pep Guardiola expressed hope his players would learn their lesson after losing their 100 percent season record in a spectacular 3-3 Champions League draw at Celtic.
Aiming to equal Tottenham Hotspur's English record of 11 straight wins at the start of a season, City had to come from behind three times to earn a point in Wednesday's Group C clash in Glasgow.
City reached the semi-finals under Manuel Pellegrini last season, but not for the first time, Guardiola pointed to their current shortcomings as a sign of their callowness in continental competition.
"This club was 25, 26 years without playing in Europe and last year was the first time to go further than the quarter-finals," he told reporters at Celtic Park.
"So that will be a good lesson. Europe is special, teams are so strong. It doesn't matter where. The opponent here, Celtic, is an amazing environment, with the fans, and we knew that.
"We had many, many chances to win the game. We scored three goals in Europe away and we created three or four more clear chances.
"So it's a pity, but that is the best way to learn. In Europe you cannot concede because they are machines. When you concede, when you make mistakes, they are there to punish you."
City, the Premier League leaders, return to domestic action at Tottenham on Sunday, but Guardiola admitted thoughts would soon turn to the forthcoming double-header with his old club Barcelona.
"I said to my players in the beginning, in this group we'll decide if we're able to qualify for the next round in the last game," said Guardiola, whose side trail Barcelona by two points.
"When you play against Barcelona, it will be tough, but now we try to analyse what we did and we're going to see what happens in Barcelona and after at home.
"We are now second; we have chances, still. We're going to recover well, to focus on White Hart Lane, and we have time to think about Barcelona."
French striker Moussa Dembele, 20, was Celtic's star man on a boisterous night at Celtic Park, twice putting the home side ahead.
Celtic 'a huge club'
But his third-minute opener was matched by Fernandinho and after Raheem Sterling had atoned for an own goal with a goal of his own, Dembele's second -- a flying volley -- was cancelled out by Nolito.
"We're very fortunate to have him," Celtic manager Brendan Rodgers said of Dembele, who was released by Fulham earlier this year.
"He was coveted by a number of teams, but his agent is a clever guy. Does he go to a so-called better league, a more competitive league, and sit on the bench and not get so many games?
"Or does he come to a big club with the opportunity to play and develop?
"You saw tonight, he really bullied the back four of Manchester City. But he's more than that.
"He's got a wonderful touch. You see his agility for the third goal. He's got power, he's got pace. He's a huge talent and he was outstanding tonight."
Celtic were humbled 7-0 by Barcelona in their opening game, but Rodgers felt the quality of their pressing and attacking football against City proved they belong in this company.
"Manchester City have travelled around the English Premier League and absolutely destroyed teams, both in terms of pressing and their football," said the former Liverpool manager.
"We've all seen it, hence everyone thought it would be hugely difficult for us. Hopefully the performance tonight shows this is a huge club.
"It just doesn't have the platform of English Premier League clubs. This is one of the biggest clubs in the world.
"In order to keep improving, we need to be at this level, but we need to perform to be at this level. It's a huge pat on the back for the club, for the atmosphere and for the players."