Fabio Borini completed AC Milan's triumph over Ludogorets Razgrad, with a 1-0 home victory capping off a 4-0 aggregate win.
Borini scored following a counter-attack in the 21st minute, turning in a Patrick Cutrone cross at the far post.
"I am happy we kept a clean sheet, as that's something I was focusing on in training lately," coach Gennaro Gattuso told Sky Sport Italia.
"It's good that nobody had a cramp after 90 minutes, but it's about attitude too. I am very, very happy with the growth...