Glasgow fall behind Stormers in bid for home URC quarter-final following defeat
Warriors went into the fixture in third place, with the top four earning home advantage in the first play-off round, but they have now been leapfrogged by their four-try hosts.
Libbok missed the target with an early penalty and it was Glasgow who drew first blood when Dempsey crossed at the end of the opening quarter.
After hooker Johnny Matthews was stopped just short following a barnstorming run down the left wing, Warriors were rewarded for turning down three points when Dempsey eventually found a way over, with Ross Thompson adding the extras.
The visitors had lost winger Kyle Steyn to injury four minutes earlier and saw their lead reduced to four points when Libbok opened his account shortly after the half-hour, before an excellent try had the hosts in front.
Damian Willemse received the ball wide on the left but drifted back inside, patiently seeking the right pass, and found Pretorius picking the perfect line to breach the Glasgow defence and touch down.
Libbok made it 10-7 from the tee and added a penalty after a subsequent onslaught failed to deliver a second try.
Pretorius, who came off worse after making a crunching tackle in the first half, did not emerge for the second and Scarra Ntubeni followed him to the treatment room after pulling up with an apparent calf issue.
The injuries did not subdue the home side, however, with Jantjies going over after taking the inside pass from Hacjivah Dayimani and URC top try scorer Zas crossing in the left corner for his 10th of the season.
Glasgow lost Josh McKay to the sin bin 12 minutes from time to end any lingering hopes of a Warriors fightback, and Roos powered over for the bonus point in the final minute, with Libbok adding the conversion.
Join free and tell us what you really think!Join Free