Complex sentence: In the 2005--06 season, he hired Ronald Koeman as manager with whom they won the Portuguese Super Cup and went to the quarter-finals of the UEFA Champions League, knocking out the defending champions Liverpool.
Split into simpler sentences: In the 2005--06 season, he hired Ronald Koeman as manager. Benfica won the Portuguese Super Cup and went to the quarter-finals of the UEFA Champions League, knocking out the defending champions Liverpool.