Replacements: Cathal O'Flynn, Keith Donoghue, Simon Crawford, Ronan Dillon, Kieran Butler.
Replacements: Liam Hyland, Risteard Byrne, Jordan Coghlan, Jamie Glynn, James Thornton.
But Clontarf had the match winner in Joyce whose excellent run of penalties - he kicked six in all - supplemented a converted penalty try in the second half.
UCD fought until the bitter end with a fortunate try from replacement Liam Hyland, after an Earls penalty had come back off a post, closed the gap to 19-16.
However, Andy Wood's men, whose defence was top notch, managed to hang on despite losing replacement Simon Crawford to a red card for a high tackle.
Two closing penalties from man-of-the-match Joyce wrapped up the result for the hosts, who are now in pole position in the division after five rounds. UCD arein second, just a point behind, following their first defeat.
Full report to follow...
Referee: Peter Fitzgibbon (IRFU)