Substitute Yussuf Poulsen's added-time goal against Greece took Denmark to the UEFA European Under-17 Championship finals and the goalscorer told UEFA.com: "This is the best feeling of my life."

As the game between Denmark and the elite round Group 3 hosts reached the 80-minute mark, the 0-0 scoreline meant the Republic of Ireland were pipping both teams to the finals in Serbia from 3 to 15 May. But then Poulsen, a 55th-minute replacement, headed in to secure Denmark's first U17 qualification since 2003.

Greece began the match in Komotini ahead of Denmark on goal difference – and on the front foot. On 31 minutes an Alexandros Mouzakitis header was saved by Oliver Korch, before the Denmark keeper blocked another header, from Vangelis Anastasopoulos, from Mouzakitis's fine right-wing cross. Not long afterwards, though, Greece lost defender Vassilis Karagounis to a second booking, with coach Theodoros Pachatouridis then dismissed.

With Ireland heading for victory against Latvia, both sides knew they needed a win. On the hour mark Stefanos Kapino, who had kept goal for Greece in last year's finals, saved Kenneth Zohore's close-range header and the home custodian made another fine stop on 74 minutes from the same player's powerful shot.

The hosts came agonisingly close themselves on two occasions late on, when Angelos Dimitriou's header was cleared off the line by Nicolai Johannesen and Charis Mavrias fired narrowly wide. However, the final word would go to Poulsen, brought off the bench 25 minutes earlier, as he nodded past Kapino in stoppage time.

"This is the best feeling of my life," the Lyngby BK forward said. "To know that I scored the goal that got us through to the finals is something I will never forget. It was such an intense match, both teams wanted to win so badly. I am not thinking about the finals yet. Let's just enjoy this dramatic qualification."

Thomas Frank's team will discover their group opponents when the final-tournament draw is made in Belgrade on 5 April, with hosts Serbia and the Czech Republic also through. The coach said: "We were the best team in the group, but we failed to reach our peak in any of the three matches. Yet we deserved to go through and it's a huge relief. The last five minutes of the game, knowing the Irish were almost through after scoring four against Latvia, were hell.

"My team have great potential and I am certain that in the finals, where they will not have the stress of qualification, they will be at their best. I trust in my players' abilities and know they can beat the big teams."