Complex sentence: Since the summer of 2002, they dominated the top four spots, thus places in the UEFA Champions League, winning all but one of the top four places between 2003--04 and 2008--09.
Split into simpler sentences: Since the summer of 2002, top four places have ensured qualification for the UEFA Champions League. They dominated the top four spots, thus places in the UEFA Champions League, winning all but one of the top four places between 2003--04 and 2008--09.