Italy U21 coach Gigi Di Biagio was frustrated, despite their 3-0 win over Slovenia.
Atalanta forward Monachello came off the bench and scored twice in the second half.
“It was very similar to the first leg, so we need to raise the tempo and play better. We created a lot, but are still not close enough to what I'd like.
“Nonetheless, it is an important result and another three points in the table," Di Biagio told Rai Sport.