However two tries in as many minutes from Danny Grewcock and Andy Beattie both converted by Olly Barkley put the visitors 14-5 in front.
A period of pressure initiated by a good Shane Byrne break ended with a Glen Jackson penalty for Saracens and moments later with numbers over, and a try looking on, Saracens glee turned to horror when David Bory intercepted to race half the length of the field and score under the posts (21-8).
From the restart slick handling and neat footwork sent Penney in for his second try and when Bath messed up the restart by kicking straight into touch Saracens attacked from the scrum and Joe Maddock but beat Dan Scarborough to the touchdown.
Next up for Saracens was Thomas Castaignede to breach the Bath defensive line and when he was hauled down just inside the Bath half, the penalty was conceded and Jackson knocked over a massive kick to leave his side trailing by just three points (21-18).
However deep in injury time Bath struck again, out-half breezing through half-hearted defence to score his side's fourth try, Barkley converting to leave Bath 28-18 in front at the interval.