Massimiliano Allegri's side have not lost in the league in 15 matches stretching back to November 27 and host the Spaniards in Turin next Wednesday in a last-16 second leg tie which is balanced 1-1. The visitors could thank Sampdoria's Japanese international Maya Yoshida for their first goal. The defender inadvertently bundled in a Juan Cuadrado cross after 23 minutes.
Moise Kean earned a penalty for Juventus, which Morata converted nine minutes later.
Sampdoria missed a chance to pull a goal back with quarter of an hour to go with Juve keeper Wojciech Szczesny denying Antonio Candreva from the spot. But Abdelhamid Sabiri put Sampdoria on the scoreboard with six minutes to go with a deflected freekick before Morata got his head to a Locatelli cross late to seal all three points for the visitors.