A terrible performance from the Glens at Neilston saw the visitors throw away a 3-1 lead.
On a rain soaked afternoon, there were no excuses about players missing, because the young Glens were just not good enough on the day, in this Scottish Cup third round meeting.
The game started badly when a defensive mix-up allowed the home forward to run in and make it 1-0 after only five minutes.
It was the spur that the Glens needed and after 10 minutes it was 1-1.
The ball broke in the area and when it fell to Thomas Houston he screwed the ball over the keeper and into the back of the new.
Three minutes later it was 1-2 with Ross McNeil striking the ball past the keeper to put his side in front for the first time in the game.
On 21 minutes the game should have been dead when Ross McNeil was tripped in the box but unusually he screwed the penalty well wide.
It was 3-1 on 41 minutes, and again Ross McNeil was on hand.
The second half was the worst 45 minutes produced by the young Glens this season, but credit goes to Neilston for fighting back.
There was a battle going on in the middle of the park, that was now becoming bogged down, but twice Neilston struck to force a replay.
On 70 minutes it was 2-3 and with seven minutes left it was 3-3, both shocking goals for the Glens to lose.
The Glens had two chances in the final minutes but Ross McNeil struck the post and former Harmony keeper Mark Baird pulled off a great save from Calum McRobbie to earn the replay that was the correct result, given Neilston’s efforts.
The rematch will now take place at the Glens on Saturday and the club will be hoping for a much better performance.
After the match the Glens coaching staff described the performance as embarrassing and not one that will be accepted at the club.
Glencairn 21s: Alan McLenaghan, Thomas Houston, Johnny Boal, Jordan Dalzell, Euan Conroy, Del Esplin, Nad Zeb, Kevin McFarlane, Ross McNeil, Calum McRobbie, Kieran Chalmers (David Quinn).
Subs not used: Stephen Sidserf, Andy Bargh, Ciaran McDade (gk).