UCD will take a narrow advantage into the second leg in Norway after they came back from behind to beat Molde FK in the UEFA Youth League.
Molde captain Leo Oestigaard gave the away side an early lead but two goals in as many minutes from Luka Lovic and Sean McDonald at the end of the first half saw the home side over the line.
The Norwegian side were positive from the beginning and deservedly went ahead in the 13th minute.
Molde caused problems from corners early on and when Simen Hagbø's corner wasn't dealt with, Oestigaard was there to finish from close range.
It took UCD to settle in front of a strong crowd at the UCD Bowl as both Neil Farrugia and Conor Crowley had shots saved just past the half-hour.
The home side flipped the game on its head in the final two minutes of the half.
Firstly, Crowley's 25-yard free-kick from the right was only parried out and Lovic was able to finish through a crowd of bodies in the 44th minute.
Less than 40 seconds later, the hosts were ahead.
Molde defender Elias Mordal gave away possession to striker McDonald, who rushed onto goal and finished under the keeper Jonatan Byttingsvik.
The visitors pressed for an equaliser throughout the second half with efforts from Christian Dahl and Eman Markovic but failed to trouble UCD keeper Conor Kearns.
UCD almost added to their advantage in the final moments of the game as captain Andrew O'Reilly burst through two players to go clean through but Oestigaard did well to come back with a late-ditch tackle.
The Students travel to Norway for the second leg on Wednesday, October 18.
UCD AFC: Kearns (GK), Farrell, Dignall, Manley, Boore, Lovic, Quinn (Hannigan 90), O'Reilly (C), McDonald (O'Keane 89), Crowley (Ryan 74), Farrugia.
Subs: Prenter (GK), Byrne, Rowe, Meaney.
Molde FK: Byttingsvik (GK), Mordal, Breivik, Oestigaard (C), Svendsen, Gussiås (Langset 79), Dahl (Hestad 74), Moe, Hagbø, Svendsen, Markovic.
Subs: Raestad (GK), Wenaas, Jenset, Ranheim.
Referee: Iwan Arwel Griffth (WAL)