Johnny McMurray's 90th minute header halted Glenavon's seven-game winning streak as Ballymena United clinched a 2-1 win at a rain-soaked Showgrounds.
Glenavon looked to have secured a point when Mark Sykes cancelled out Andy McGrory's first-half opener before McMurray's late winner.
It was Glenavon's first defeat since the opening day of the season.
Crusaders secured a 3-0 win at Newry City with a Rory Patterson penalty and two late goals by Paul Heatley.
Stephen Baxter's side have climbed above Cliftonville into fourth place in the table but the defending champions have played two games more than the three teams below them.
Ballymena remain in third place but David Jeffrey's side have closed the gap on the top two in the table while the defeat for Glenavon has given Linfield the chance to regain the lead in the title race when they host Warrenpoint Town at Windsor Park.
Sky Blues shine under dark skies
In testing conditions at the Ballymena Showgrounds, the home side were the first to settle despite playing into a swirling wind and a persistent downpour.
Glenavon's Andy Hall almost took advantage of those conditions when the ball fell to his feet just six yards from goal but it was the Sky Blues who took the lead seconds later when Cathair Friel hung up a cross in the breeze and James Knowles headed into the path of the unmarked McGrory, who made no mistake from close range.
The home side were creating problems for the Glenavon defence with Adam Lecky, William Faulkner and Friel causing havoc down the left wing and Faulkner flashed a shot just wide of the posts after sprinting onto Lecky's audacious back-heel flick.
The conditions became increasingly difficult in the second half and the Lurgan men began to enjoy greater possession as they pressed for an equaliser but Ballymena still looked the more dangerous on the counter-attack.
Lecky was inches away from connecting with a low cross by Knowles - Glenavon's Caolan Marron getting a vital touch to divert the danger - and the ever-dangerous Friel could not get enough loft on his shot after he spotted Jonny Tuffey off his line.
Sykes was becoming increasingly influential for Glenavon and his quick footwork fashioned a chance for Stephen Murray but the striker flashed his shot over the crossbar.
The visitors drew when Ballymena were momentarily down to 10 men following an injury to Faulkner with Sykes picking up the ball just inside the penalty area and firing a low, swerving shot past the dive of Ross Glendinning.
In an end-to-end finish to the game, the Sky Blues appeared to have spurned a late chance to snatch all three points when Lecky took too long to line up his shot and Marron made another sliding block.
McMurray's introduction off the bench had given the home side an extra outlet in attack and the big striker was perfectly positioned to plant home Tony Kane's hanging cross as the game ticked towards injury-time.
Crues get back to winning ways
Crusaders bounced-back from their 3-0 humbling by Ballymena with a similar rout of struggling Newry City, who are now just a point above bottom-of-the-table Dungannon having played two games more.
Crues' manager Baxter responded to his side's defeat last week by making several changes, recalling fit-again Heatley and also handing a start to Harry Doherty ahead of regular goalkeeper Sean O'Neill.
Doherty was called into action during the opening stages to deny Stephen Hughes, Declan Carville and Mark McCabe in a lively start by the home side.
The visitors dominated the second half and took the lead within five minutes of the restart when Patterson drew a penalty from a clumsy challenge and the former Derry City striker converted from the spot.
Newry's Stephen Teggart forced another superb save from Doherty before Crusaders doubled their lead with just over 10 minutes remaining when Heatley punished a sloppy defensive header to fire a shot through the legs of Steven Maguire and the forward wrapped up the scoring in stoppage time when he calmly finished off a one-on-one chance.