Four first-half tries meant Bath were well on their way to a double over their Welsh rivals in Pool Two and they ended up with a 30-13 victory that made it five wins in a row in the tournament.
The Dragons were hampered by a series of injuries to key players in a blistering first half that saw Micky Young launch Bath's scoring sequence with a sixth-minute try. Tom Biggs followed suit and then Mat Gilbert and Leroy Houston brought up the bonus point in 31 minutes.
The home side could only muster two penalties from replacement outside-half Steffan Jones in the first half as they trailed 27-6 at the break. They grabbed a consolation try in the second half through Nic Cudd, which Jones converted.
Andrew Fenby ran in a first-half hat-trick of tries as London Irish went on the rampage in their Pool Five clash with Portuguese outfit Lusitanos. The Exiles were 36-3 ahead at the break and ended up 79-3 winners.
There were 13 tries in all, with Tom Fowlie and Guy Armitage both grabbing two, and seven conversions. Qualification for the quarter-finals will go down to the final round of matches, but Irish will have to hope Stade Francais Paris trip up against Lusitanos.
The Exiles travel to Stadion Enrico Chersoni to tackle I Cavalieri Prato in round six but Stade will qualify for the quarters if they and Irish finish level on points at the end of the group stages, courtesy of the fact that they picked up more match points in their head-to-head encounters.
Oyonnax dented Biarritz's hopes of winning Pool One as they notched a bonus point win on home soil, 28-24. That win gave pool leaders Sale Sharks a massive boost in their quest to reach the last eight.
Sale have to travel to Biarritz in round six and will make the trip armed with a four-point cushion. They beat Biarritz at home in round one.