A Robbie Smith goal midway through the first half put Paul Osam's Under 21's into 3rd round of the Enda McGuill cup.
In a close game in the AUL in Clonshaugh UCD had the better of the first half without ever really threatening Brendan Clarke's goal.
The second period saw the Saints, under the watchful eye of newly appointed U21 manager Paul Osam and his evergreen assistant Cyril Walsh, come more into the game.
The breakthrough came on the hour mark when Smith was quickest to react when the ball came back off the UCD crossbar, he ducked down bravely to head the ball home and took a boot in the face for his troubles.
Team: Clarke; McMahon, Sargeant (Fitzsimons), O'Shea, Bell; Doran, Maher, Perth, Foley M.; Smith, Olina (Fitzpatrick).