Last year, it was the virtuoso display of Philip Stirling that broke their hearts, the Lisnagarvey striker bagging a memorable hat-trick to lead the Northern side to a 3-2 victory.
And this year, another Ulster club are threatening to shatter Harlequins' dreams.
Instonians have had a strange year. The Ulster league seemed to be their main focus, but as that left their grasp, the Senior Cup and Club Championships are the two targets that remain in their sights.
All this in what is considered a re-building year. “I know how people can get that impression that we were in re-development this year with all the young players coming into the team,” captain Mark Wainwright says. “But even though we had four schoolboys in our panel, there was still plenty of experience there, too.”
On Sunday, Instonians are expected to start with three of the four schoolboys for the decider from Belfield. But having so many youthful talents out on the big day doesn’t concern Wainwright or his team.
“All four schoolboys have played a very important part in our run to the Senior Cup final,” the skipper said.
“Stephen Redpath and Paul Gleghorne have been particularly excellent. Inexperience wouldn’t be a worry for us.
“We have the right blend, there are a lot of players who have played on the big occasion before, like Neil Cooke and Mark Irwin.
“So, there is a lot of older heads on the team. I think the energy of the young lads has kept those of us with more experience on our toes.”
Three of the four schoolboys on the squad will fly out with the schools team on Monday to Barcelona for a tournament, and they hope to have medals in their back pockets.
“We have played a couple of times recently and they are a difficult team to play against. They are undoubtedly one of the best teams around at the moment,” Wainwright asserts.
“Even though they are physical, they are also a talented side and tend to hit you on the break when they are playing defensively. With the likes of David Eakins around, we will have to keep our concentration.”
Harlequins have four Irish internationals on board, including goalkeeper Wes Bateman and defender Jason Black, and with Eakins involved too they are likely to have a big impact.
For example, Inst's prolific penalty corner marksman Chris Barnes will be up against Bateman, and at the other end Eakins will be testing Inst keeper Johnny Burns. Black is also likely to be facing international colleague Mark Irwin, all of which should make for a series of interesting confrontations.
As Wainwright says, this is an excellent chance to gain a European spot. “The focus always changes to the club championships at this time of year, but with the Senior Cup, it is an extra chance to get into Europe.”
Coach Paul Cooke is aware Harlequins have a video from last week's league clash against Banbridge, but having lost that game 1-0, he's hoping they haven't gleaned too much from those team tactics.
“There can’t be anything read into that performance,” Wainwright says.