Rodrigo Palacio fired the Serie A outfit in front inside five minutes, but Naldo pulled hosts Wolfsburg level before the break.
And Kevin De Bruyne's second-half brace ensured the Bundesliga side head to San Siro for the second leg next Thursday with a two-goal advantage.
"It's a shame, of course," Ranocchia told Mediaset Premium. "But we've still got the second leg. This evening we scored an away goal and we need to make that count.
"We still have another 90 minutes to qualify. We made too many naive mistakes. We started really well and it was not easy.
"We absolutely believe we can qualify. It is not over."
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