Goals from Matthew Fitzpatrick and Gregory Moorhouse earned Glenavon victory from this trip to the Showgrounds to face Ballymena United.
Fitzpatrick opened the scoring on 13 minutes with a low finish past keeper Ross Glendinning after Peter Campbell's turn inside the box created space to lay the ball off.
Ballymena might have levelled just after the half-hour mark when a run by Trai Hume ended with his effort beating Johnny Tuffey only for the ball to come back off the post.
Robert Garrett almost doubled Glenavon's lead early in the second half but his close range shot blazed over while, around the hour, Shay McCartan sent a free-kick just wide at the other end.
Daniel Purkis was a threat for Glenavon, coming close twice in a few minutes but was denied by Glendinning both times.
United pressed for the equaliser as the game moved into the closing quarter-of-an-hour with Leroy Millar forcing a save from Tuffey and then James Singleton almost turning a Tony Kane corner into his own net.
But, three minutes into stoppage time, Moorhouse made sure of Glenavon's win with a calm finish after Conor McCloskey had played him into space.
Ballymena United: Williamson, Redman, Addis, Winchester, Harpur, McElroy, McCartan, Waide, Hume, Millar, C. Kelly subs Glendinning (not used), T. Kane (replaced Harpur 82), K. Kane (not used), Balmer (not used), Ervin (not used), J. Kelly (replaced Redman 65), McCready (replaced Waide 46)