He made his debut with Inter on the first matchday of the 1997–98 Serie A season, on 31 August 1997, against Brescia, at the Giuseppe Meazza Stadium. His most notable and successful career spell came with the Milan club, and in his first season, he won the 1997–98 UEFA Cup under manager Luigi Simoni, notably scoring a goal from a bicycle kick against the Swiss team Neuchatel Xamax during the tournament. Inter also narrowly missed out on the Serie A title to Juventus that season, as Moriero made 28 league appearances that season, scoring 3 goals. Although he made fewer appearances during the next two seasons due to injury (making 28 appearances in Serie A in total, scoring 3 goals), he also later reached the 2000 Coppa Italia final with the club, under Marcello Lippi, before moving to Napoli in 2000. During the 2000–01 Serie A season, he made 14 appearances with Napoli, scoring a goal, although he was unable to save the club from relegation. He ended his career with the club in 2002, in Serie B. In total he made 287 appearances in Serie A, scoring 21 goals.