After José Mourinho was hired as Porto manager, Postiga became a first-team regular. The 20-year-old scored 19 times in 2002–03 playing alongside Derlei, as Porto won the treble. This included 13 in a victorious league campaign as well as five in an eventual conquest of the UEFA Cup, although he missed the final due to suspension. Following his successful season, he made his senior international debut for Portugal.