Oscar looked set to enjoy a dream European debut after scoring a stunning first-half double against Juventus but the Italian champions ruthlessly exposed the holders' defensive deficiencies to snatch a Group E draw at Stamford Bridge.
They were even a lick of paint from completing a sensational turnaround as Blues boss Di Matteo's acknowledgment that retaining the trophy could prove mission impossible seemed to prove prophetic.
He said: "We feel disappointed and a little bit deflated that we found ourselves in a fantastic position to win this game and we came away only with a draw.
"We should have closed the game and brought the win home."
Chelsea's defending was bad enough when Juve pulled a goal back through Arturo Vidal before half-time.
But just when it looked as if the holders had done enough to hang on, they went missing again, with John Obi Mikel giving the ball away and failing to track back and David Luiz in no man's land as Fabio Quagliarella waltzed through to level.
Di Matteo said: "I think we should have dealt with it a little bit better. There was no pressure on the ball and it was pretty difficult to play offside.
"We lost possession just beforehand and we should have reacted much quicker to losing the ball than we did."
He added: "It's something that you try to improve all the time, to be composed in possession and to keep the ball better.
"We did during the game give the ball away a little bit too cheaply at times but I think we also played some good stuff tonight [Wednesday]."
Much of that "good stuff" came from Oscar in a sensational two-minute spell just past the half-hour mark.
Di Matteo raised eyebrows by handing the £25 million Brazil star his full debut but it proved an inspired selection.
The 21-year-old's opening goal owed a lot to the kind of luck Chelsea enjoyed in spades en route to their Champions League triumph but his second was the kind of spectacular strike that would have had billionaire Roman Abramovich drooling.
Di Matteo said: "It was a great debut for Oscar. I thought it was the right game to start him and he did a perfect job tactically.
"He scored two goals and the second one was a wonderful goal.
"He is a big talent. He has got a bit of everything.
"We shouldn't forget that he is still a young man - he is only 21 - but he is already quite established in his national team already.
"I think we are very lucky to have him in our team."
Oscar's contribution was curtailed when he was hurt making a tackle on Leonardo Bonucci, who appeared to stand on him as he landed.
Di Matteo endorsed calls for UEFA to examine video footage of the "bad tackle", criticising the performance of referee Pedro Proenca.
"The referee tonight did do nothing about many challenges. The game has finished now for us.
"If UEFA has a look then good. But we have to move on from it."
He added of Oscar: "We will have to assess him tomorrow [Thursday] morning but he got a knock on his ankle."
Di Matteo was also far from impressed by Proenca's failure to award Eden Hazard a penalty after a clumsy challenge by Andrea Barzagli when the score was still 2-1.
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Hazard was also denied a spot-kick in Saturday's goalless Barclays Premier League draw at QPR and Di Matteo said: "It's a penalty. He got pushed and there was contact as well.
"It's the second game in a row now that they seem to not see it."
The Chelsea boss played down a hamstring injury to Daniel Sturridge that left Fernando Torres as his only recognised striker on Wednesday night.
He said: "He won't be out for long. We'll assess him again tomorrow."
Juventus' fightback showed just why they have gone 42 Serie A games without defeat.
The introduction of Quagliarella during the second half proved as inspirational as Oscar's selection for Chelsea, the substitute also hitting the crossbar.
Assistant boss Massimo Carrera, in charge while Antonio Conte sat in the stands as he serves a 10-month ban, insisted the change was his own decision.
He added: "We could have won it, we could have lost it but that's football.
"We stepped it up and we just proved tonight we can play European competition at this level."