A 79th-minute header by substitute Marcus Kane gave Glentoran victory over Portadown in the Irish Cup semi-final.
Kane rose in a crowded penalty area to get on the end of Richard Clarke's corner from the left.
Earlier Portadown could have taken the lead but Darren Murray lobbed a good chance wide and Kevin Braniff had a shot blocked in the penalty box.
Cliftonville's win in the other semi-final means Glentoran have secured a place in next season's Europa League.
The Glens had the best chance of the first half when Jay Magee missed a heading chance and soon after that Stephen Carson saw a shot blocked.
The Windsor Park victory is a sweet moment for the Glens and their manager Eddie Patterson - and will also help ease their financial worries.
It has not been an easy season for the east Belfast club as they have had to deal with cash flow problems. At one stage, players refused to attend training sessions because they had not received their wages.
For Portadown, it is effectively the end of a disappointing campaign.
The Ports, runners-up in the Premiership last season, failed to finish in the top half of table this time and have now missed out on the cup showpiece.
Afterwards Kane, a former Linfield player, spoke of his special match-winning moment.
"It is just unreal, coming back to Windsor Park and getting a result which put the smiles on our fans' faces," he said.
"They have supported us through difficult times this season and it is very special for me.
"I just attacked the near post. I did not actually see it go in, but I am pretty sure it was my goal. It is the best feeling."
Manager Patterson revealed Kane had come on as a substitute as winger Carson had been ill on the night before the match.
"We decided to take a chance on Stephen and gave him an hour," said the Glens boss.
"Marcus came on and certainly didn't let us down."
Patterson was savouring reaching the cup final in his first full season in charge.
"I am delighted for the players after all they have been through this season," he said.
"I was brought to the club to help them challenge for trophies. We are a work in progress, this is a young squad."
Glentoran: Morris, Hill, Magee, Callacher, Ward, R Clarke, M Clarke, McAlorum, Howland, Waterworth, Carson (Kane 74).
Portadown: Miskelly, Redman, Ramsey, Breen, Casement (Burns 83), Mackle, Mouncey (Lecky 90), McNeill, McCafferty, Murray (Twigg 61), Braniff.