An own goal by debutant goalkeeper Patrick Jennings handed Dungannon Swifts all three points in Thursday's Premiership clash at Mourneview Park.
It happened in the 84th minute when Nial Henderson curled in a corner and Jennings, son of NI keeping legend Pat, punched the ball into his own net.
That was just two minutes after Dungannon had equalised when sub Ryan McIlmoyle ran through to shoot in.
Glenavon had led through a 20th-minute goal by Ryan Harpur.
He headed in at the far post after new boy Chris Lavery's deep cross from the left.
Early in the game Jennings had done well to tip over a 25-yard effort from Henderson.