Roberto Di Matteo admitted Chelsea only had themselves to blame after watching them blow a two-goal lead to open their defence of the Champions League with a 2-2 draw against Juventus.
Oscar looked set to enjoy a dream European debut after scoring a stunning first-half double but the Italian champions ruthlessly exposed the holders' defensive deficiencies to snatch a Group E draw at Stamford Bridge, with Arturo Vidal and Fabio Quagliarella on target.
Di Matteo 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 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 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."
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 £25million 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."