Paulo Fonseca wants defensive improvement from Milan after they almost let their lead slip in a 3-2 Champions League win at Slovan Bratislava on Tuesday.

Milan secured a third consecutive Champions League win but had to hang on as the hosts pulled a goal back in the 88th minute and pushed for a leveller.

While Fonseca was delighted that his side moved on to nine points, the Portuguese coach pointed out his team's defensive errors that led to the late drama.

"We have won the last three games in the Champions League. We have scored nine goals. It is very positive. Today it was important to win, and that is what we did," Fonseca told reporters.

"I think we dominated during the match. We changed a lot of players. We did some positive things but also some things to improve, maybe because we changed a lot of players.

"We didn't do the defensive marking well, then after the break, we improved. We deserved to win."

Slovan only had six shots, yet accumulated 0.97 expected goals (xG), suggesting they created some high-quality chances.

Christian Pulisic put Milan ahead after 21 minutes, but Tigran Barseghyan swiftly dragged the home side level.

Rafael Leao became the first half-time substitute to score in the Champions League for Milan with his goal the 500th scored in the competition by Portuguese players, and Tammy Abraham netted what proved to be the winner three minutes later, with Nino Marcelli's late effort ultimately not enough for Slovan.

Fonseca added that he did not see a problem with his players' attitude, but rather in their reading and understanding of the game when defending.

"These things are difficult to explain. Maybe because these defenders haven't played much. It's a question of reading, not of attitude," he said.

"In the first half, when we allowed Slovan to come out, it was a question of defensive marking. We were too far away with the defenders, and they were always alone to come out. It's a problem of reading and understanding what was happening."

Milan moved up to 14th in the standings, with nine points from their five matches.