Crusaders’ league lead at the head of the Danske Bank Premiership now stands on goal difference alone as Glenavon battled back to rescue a point that could prove a season-defining day in the title race for challengers Coleraine.
With the injured Jordan Owens and absent Darren Murray out of contention, Sean Ward stepped forward during the early exchanges as the main Crusaders attacking threat with a number of efforts from distance.
The first, a dipping drive from around the 30-yard mark, bounced off the crossbar before firing goalwards with an angled hit.
Jonny Tuffey was, once again, called into action during the hosts’ effective start to save at a stretch off Michael Carvill’s curling shot from the left-hand side of the penalty area.
Colin Coates raced in towards the back post but knocked wide off Paul Heatley’s corner-kick delivery as Crusaders increased the pressure in pursuit of the upper hand.
It is understood that Murray was named on an early teamsheet but his absence forced the Crues into a late reshuffle.
However, Heatley stepped up on 29 minutes with his 25th goal of the season to break the deadlock and reward Stephen Baxter’s side for a strong start.
Glackin and Heatley combined on two occasions in one flowing move to cut open the Glenavon backline, with the latter showing composure at the end to move past the out-rushing Tuffey and pick his spot despite the presence of two players on the line.
Glenavon’s depleted line-up lacked an attacking response before the break with the exception of Josh Daniels’ header over the bar off Rhys Marshall’s cross and a penalty shout following an incident between Colin Coates and Mark Sykes.
Tuffey was at the heart of the second-half action two saves to deny Heatley then Glackin.
However, Glenavon came close to an equaliser on the hour mark when substitute Marc Griffin found some space in the box following a driving run by McGrory but back-tracking Philip Lowry’s key block took the sting out of the shot.
Glenavon survived thanks to a combination of resolute defending and rapid reactions as Jordan Forsythe’s first shot was blocked by Marshall then Tuffey dropped low to deny the second attempt before Andy McGrory deflected away Heatley’s rebound strike.
And Crusaders’ failure to cement control resulted in what could prove a memorable moment on 76 minutes as Sykes’ run along the left resulted in a cross which Andrew Mitchell managed to hook home.
David Cushley came close to a match-winning cameo but, at a stretch, was unable to gain a touch to convert Matthew Snoddy’s low sweeping cross off a clever Heatley backheel.
Robbie Norton - who marked his senior Glenavon debut at the same ground on the final day of last season with a goal - then hit the crossbar in the closing moments.
CRUSADERS: Jensen, Burns, Coates, Beverland, Ward, Lowry, Caddell (Snoddy, 51), Glackin (Cushley, 71), Heatley, Forsythe, Carvill (Bonner, 82).
Subs (not used): McClean, McChrystal.
GLENAVON: Tuffey, Burns, Doyle (Norton, 43), Daniels (Kelly, 79), Marshall, Mitchell, Sykes, McGrory, Cooper, Murray (Griffin, 46), Singleton.
Subs (not used): Foley, McCavitt.