The New Zealand international opened his account in the 15th minute when Broncos young gun David Fifita dropped the ball and Proctor grubbered twice before diving over.
When Brisbane fullback Darius Boyd spilt a Taylor grubber seven minutes later, it was Proctor who got there first again.
Brisbane began their comeback just before halftime, with Glenn latching on to a forward-looking Kodi Nikorima short-ball to cruise over.
Glenn made it two 10 minutes into the second half when he collected a smart grubber by five-eighth Sean O’Sullivan and then levelled the match in the 64th minute after again running on to a Nikorima short ball.
The Broncos then hit the front when Isaako stepped through Ryley Jacks and Jarrod Wallace before sprinting 60m and finding Nikorima, who then sent Kennar over.
Isaako’s late field goal sealed the victory, before Jesse Arthars scored a late consolation for the home team.
Brisbane begin their NRL season at Melbourne on March 14 while the Titans host Canberra on March 17.