Complex sentence: The third season started in 2007 with 735,000 viewers, Season Four premiered in 2008 with 720,000 viewers while season five in 2009, opened with over 800,000 viewers, the highest of all previous season debuts.
Split into simpler sentences: The third season started in 2007 with 735,000 viewers. But Season Five in 2009, opened with over 800,000 viewers, the highest of all previous season debuts.