The hosts led 28-9 after 25 minutes before full-back Mike Haley and replacement hooker Kevin O'Byrne put their names on the scoresheet for the two-time winner.
Later, Argentina winger Santiago Cordero celebrated a two-year contract extension with a hat-trick in Bordeaux-Begles's 47-8 hammering over the Dragons.
Earlier, joint record four-time winner Leinster went top of Pool A by overcoming a much-changed Northampton Saints 35-19.
Gloucester's 20-year-old substitute George Barton scored after four minutes of additional time to claim a 38-34 success over Ulster in the Cherry and Whites' first match since Danny Cipriani's midweek departure.
On Monday (AEDT), last season's runner-up Racing 92 heads to Harlequins and Pat Lam returns to Connacht with his Bristol Bears side, which lifted the European Challenge Cup in October.