transfer fee to the Austrians. He joined Basel's first team during their 2001–02 season under head coach Christian Gross. After playing in three test games Zwissig played his team debut in the Swiss Cup game on 17 February 2002 as Basel won 1–0 against Colombier. He played his domestic league debut for the team one week later in the away game in the Cornaredo as Basel won 5–2 against Lugano. Ironically, he scored his first goal for his new team on 4 April in the away game in the Espenmoos as Basel won 3–1 against his former club St. Gallen. Basel won the last game of the season, on 8 May 2002, and became champions ten points clear at the top of the table. Just four days later they played in the cup final against Grasshopper Club winning 2–1 in extra time they won the double. Basel's 2002–03 UEFA Champions League season started in the second qualifying round. After beating Žilina 4–1 on aggregate and Celtic on the away goals rule after a 3–3 aggregate, Basel advanced to the group stage. They ended this in second position behind Valencia, but ahead of Liverpool and Spartak Moscow to advance to the second group stage. They ended this in third position behind Manchester United and Juventus, but ahead of Deportivo La Coruña. Zwyssig played in 12 of these 16 games. Basel ended their league season as runners-up, but in the cup they advanced to the final and here they beat Xamax 6–0 to defend the title. As cup winners Basel were qualified for the UEFA Cup first round and here they beat Malatyaspor 3-2 on aggregate due to the silver goal rule. However, in the second round they lost both games against Newcastle United. Zwissig played in all four games. In their 2003–04 league season the team started well, winning their first 13 matches straight out. The first defeat came on matchday 24. Basel won the championship with 26 victories and seven draws, the team had suffered just three away defeats, and obtained 85 points. Zwissig had 30 appearances in the 36 fixtures. However in the cup the team were eliminated early, in round three, Zwissig scored a goal in the first round against FC Alle and in the second round against Urania Genève Sport. As reigning Swiss champions, Basel entered 2004–05 UEFA Champions League in the third qualifying round, however, drawn