The Italian league leaders hosted their Serie A rivals in the first leg of a last 16 tie at Juventus Stadium on Thursday, and looked on course to take an advantage into the return match when Arturo Vidal notched after just three minutes.
However, Mario Gomez popped up with 11 minutes remaining to score his first goal since returning from a long-term knee injury in February, ensuring the tie will be nicely poised when the teams battle again at Stadio Artemi Franchi next Thursday.
With Juve having beaten Fiorentina 1- 0 in the league on Sunday, goalkeeper Buffon suggested that Antonio Conte's side may have taken their lead for granted.
Speaking to Sky Sport Italia, he said: "Maybe we thought, considering in recent games we had controlled the second half well, that we could do so again.
"It is also true that it can't always go well, as we were facing a side with strong individuals who can hurt you at any moment and find that moment to change the game.
"The goal is one of those moves that can happen, especially as Gomez is a great champion. Naturally there are regrets, as we thought that we could take the 1-0 home the same way we had done on Sunday in Serie A."
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