Antonio Conte felt Chelsea had come close to playing a "perfect game" against Barcelona.
The Blues were leading the first leg of their Champions League last-16 clash thanks to Willian's strike, only for a defensive error to gift Lionel Messi an equaliser.
The goal, Messi's first in nine matches against Chelsea, means they now face an uphill task to avoid a European exit in the second leg at the Nou Camp next month.
But it was harsh on the hosts, who had limited Messi, Luis Suarez, Andres Iniesta and company to a smattering of chances while Chelsea could have been three up - Willian hit a post twice - before the Argentinian struck.
"We were very close to playing a perfect game, we paid dearly for one mistake," said Conte.
"But we know very well against opponents like these that if you make a mistake you pay.
"It's a pity because I think at the end of the game we are disappointed with the final result.
"We hit the post twice so there is disappointment, but at the same time the game must give us a lot of confidence to trust ourselves in the second leg.
"It won't be easy, we must be realistic, we are talking about Barcelona.
"But tonight we showed if we are ready to work hard together defensively and at the same time continue to have the right feeling when we have the ball, to have the chance to score, then we can try to do something incredible."
Willian rattled both posts in front of The Shed in the first half but made it third time lucky on the hour, pinging a low shot into the bottom corner.
However, Barcelona hit back with 15 minutes remaining, punishing the first mistake of the night from the Chelsea defence.
Conte, who revealed he had been having trouble sleeping ahead of the match, will be having nightmares about the equaliser.
Andreas Christensen's suicidal pass across goal left Cesar Azpilicueta scrambling in vain and allowed Iniesta to cut the ball back to Messi.
He had been denied with his last 29 efforts on goal against Chelsea, but he made no mistake with number 30.
Yet Conte refused to blame young defender Christensen, chosen ahead of the experienced Gary Cahill, for his error.
"No, absolutely no, no, no," he insisted.
"Christiansen's performance was great, incredible. He is only 21 years old, it's great that he's able to play this game with his maturity and personality.
"He was one of the best players tonight. A top, top game and I'm very pleased for his performance."
The visitors predictably dominated possession, racking up 73 per cent while making 887 passes to Chelsea's 325.
But Barca coach Ernesto Valverde said: "We still have to be respectful of their style of play. Anything can happen.
"Yes we passed the ball more. But they pressed us high and they made life very hard for us.
"The away goal is not definitive but it is important, yes."