Elsewhere, Derry grabbed a valuable point at Richmond Park, coming from two goals down against Pat's, thanks to goals from strikers Michael Holt and Gary Beckett.
UCD 3 (Sullivan 60, O’Donnell 77, Leech 90) WATERFORD 0
A twenty-yard strike from Sullivan set College up for only their third win of the season, and their thirteenth point in eleven home games.
A goal mouth scramble on the hour mark, saw the ball funnel back to Sullivan and he made no mistake driving a powerful shot through a forest of players and into Dan Connor's net for the lead goal.
A listless first half saw play very much in the middle of the field, with UCD's Alan Cawley stifled at times by the prominent Wayne Fitzgerald and Kevin O'Brien.
Midfielder Mick O'Donnell glanced home UCD's second on 77 minutes, following a great cross from Cawley, before substitute Mark Leech, son of the legendary Mick, scrambled home a third as the game moved into injury time.
Jimmy McGeough's Waterford must now contend with a blotted record of four losses in their last six games, and with a rampant Bohemians' side due at the RSC on Friday, it could just get worse. Mahon in his second game in charge for College will want to add further to the four points gained by his side in September, with a Thursday trip to the Brandywell.
ST PAT'S 2 (Delaney 28, Hutton og 31) DERRY CITY 2 (Holt 38, Beckett 45)
Dermot Keely's Derry City came from two goals behind to rescue a valuable point at Richmond Park, in their basement struggle.
The Foylesiders' first game for three weeks began brightly as the first-choice strike force of Gary Beckett and Michael Holt both had shots tipped over early on by Pat's goalkeeper Chris Adamson.
Eamon Collins' home side, missing the services of top scorer Tony Bird through suspension managed to get their noses in front as the game lulled at the midway point.
Former UCD and West Ham defender Clive Delaney managed to head home Keith Fahey's 27th minute corner for the lead goal, past Alan Gough and defender Eddie McCallion.
It turned worse for the Derry defence a few moments when a Pat's attack initiated by Charles Mbabzi Livingstone was eventually lobbed past his own keeper by a red-faced Peter Hutton.
Keely's men regrouped however, with Hutton leading the charge and a left-sided move eventually sprung Michael Holt to the edge of the area and he held off Darragh Maguire brilliantly to lobe Adamson from twenty yards, with seven minutes left in the half.
Right on the stroke of half-time, a long ball from Gough saw Delaney head clear but only to Ciaran Martyn who fed the unmarked Gary Beckett and he made no mistake with a rising drive past an unsighted Adamson from the edge of the Pat's area for the leveller.
Few chances of note came the way of either side in the second period, with Derry condensing midfield, and deservedly holding on for a draw.