Joyous Gatti tapped in the only of goal of a tight game in the 73rd minute at the Allianz Stadium in Turin to give Juve a slender lead to defend in Portugal next week.
The 24-year-old defender was on hand to poke home after Antonio Adan flapped at a deep cross and Dusan Vlahovic had his resulting header cleared off the line.
It was a positive end to a night in which Juve had to watch in worry as goalkeeper Wojciech Szczesny was checked over by medical staff following chest pain.
Poland international Szczesny was replaced by Mattia Perin late in the first half, leaving the pitch in tears after breathing problems and heart palpitations.
And Perin proved a handy replacement for Szczesny, who Juve say didn't have any serious health issues after early tests.
Former Italy international Perin pulled off a superb double save in the final seconds from Pedro Goncalves and Hector Bellerin, who both blew chances to tap the away side level at the last.
