Zebo was joined on the scoresheet by BJ Botha and Johne Murphy, while the ever-reliable Ronan O'Gara kicked 24 points to hand the RaboDirect PRO12 title holders a sixth win from as many Heineken Cup games this season.
Heineken Cup holders Leinster secured a home quarter-final thanks to a comfortable 25-3 victory against Montpellier at the RDS.
The RaboDirect PRO12 leaders raced into a 17-0 lead thanks to tries from Sean O'Brien and Rob Kearney, before Cian Healy crossed after the interval to wrap up the win, Fergus McFadden adding ten points with his boot.
Meanwhile, Ulster were not able to guarantee a home draw as they slipped to a 19-15 defeat at the hands of French outfit Clermont.
Clermont, now unbeaten in 36 home matches, were far from convincing but did enough to guarantee a return to familiar surroundings in the next round, despite five penalties from the boot of Ruan Pienaar.
Tries from Aaron Shingler and Mat Gilbert helped the Scarlets book an Amlin Challenge Cup quarter-final place with a narrow 16-13 victory over Castres, although Glasgow were not so fortunate as they fell to a 23-18 defeat at the hands of Bath.
Elsewhere, Aironi ended their Heineken Cup campaign without a single point as they were thrashed 33-6 at Leicester, two Olivier Naas penalties all they had to show from their trip to Welford Road.