The following year, she was invited to join the Romanian national team, and began working with coaches Octavian Belu and Mariana Bitang at the elite training facility in Deva.

[2] Success in major international junior meets soon followed, including a first-place finish at the Top Gym tournament in Belgium in 1999[4] and a bronze medal at the 2001 European Youth Olympic Days.

At the 2002 World Championships in Debrecen, Ban won a silver medal on the balance beam, one of Romania's only victories of the competition, and placed fourth on the floor finals.

[8] In 2003, Ban had a similarly strong showing, contributing to the Romanian team's silver medal at the 2003 World Championships and placing sixth in the all-around final.

[15] Oana's career highlight came at the 2004 Summer Olympics in Athens, where she, along with teammates Monica Roșu, Alexandra Eremia, Cătălina Ponor, Daniela Șofronie and Silvia Stroescu, won the gold medal in the team competition.

Nonetheless, she was able to perform as an all-around gymnast for the Romanian team, and posted scores that frequently placed her in the top ten at major competitions.