Tommy Lonergan's first-half strike proved decisive as UCD will enjoy another season in the SSE Airtricity League Premier Division.
The vast bulk of the 2,781 attendance trooped away disappointed from Richmond Park as their Waterford side face a second successive season in the lower tier.
Junior Quitirna should have forced extra-time in a dramatic finish to this promotion/relegation play-off decider, but missed a 94th-minute penalty as Waterford also finished with 10 men.
Having rested a host of players for last week’s meaningless final game of the regular season against champions Shamrock Rovers, regulars Sam Todd, Evan Osam, Jack Keaney and Lonergan returned for UCD.
Waterford manager Danny Searle kept faith with the same starting XI that dismissed Galway United 3-0 in the First Division play-off final at Markets Field last week.
And the Blues' free-scoring attack, which had mined 28 goals from their last 10 games, looked evident from the off.
Talisman winger Phoenix Patterson collected Shane Griffin’s pass to get the ball onto his right foot to rifle over inside two minutes.
College responded within a further minute, creating a dangerous opening with their first assault. Alex Nolan’s shot was blocked by Darragh Power to fall for Sean Brennan, who ballooned his effort over the top.
Lonergan showed his threat shortly after that, cutting inside Tunmise Sobowale to see his shot deflected into the path of Nolan who rifled not far over Paul Martin’s crossbar.
UCD’s Kian Moore was the first keeper to see real action on 12 minutes, getting down to his right to make a comfortable save from Quitirna’s deflected free kick.
If that was something of a let-off for UCD, given the Blues’ prowess from set plays, it was they took the lead from a dead-ball routine of their own for what brought the game's only goal on 15 minutes.
Having been clumsily fouled by Alex Baptiste, UCD winger Alex Nolan whipped an inviting ball into the area.
Lonergan timed his run to perfection to out jump a hesitant Martin to head home his seventh league goal of the season.
🎥 | GOAL!— SSE Airtricity League (@SSEAirtricityLg) November 11, 2022
Thomas Lonergan gives UCD the lead in the Promotion/Relegation Play-Off Final! 🥅
What a delivery by Alex Nolan 🙌📭
Watch live | https://t.co/jPdwV1Ivf4 📺#LOI | #LOITV pic.twitter.com/f9W6G6UYGj
Desperate defending prevented the Blues from levelling eight minutes later following a right scramble in the UCD area.
Todd initially blocked a shot from Shane Griffin with Yassine En-Neyah's header then cleared off the line before Patterson’s follow-up was deflected for a corner.
UCD remained the team with a better shape to them in the early stages of the second half, Dara Keane drilling wide with a snap shot early on.
Enjoying plenty of the ball, Waterford continued to huff and puff.
Centre-forward Wassim Aoucchria looked set to level on 52 minutes from Niall O’Keeffe's looped cross only to succeed in heading clear, albeit under pressure from Moore.
But it was Martin who had to make the first save of the second half as Waterford failed to clear a free kick.
Michael Gallagher headed the ball down for Lonergan who worked Martin at his near post.
With the pressure mounting at the other end, Moore then produced the save of night on the hour, parrying away a deflected shot from Patterson who had cleverly worked the ball onto his left foot.
Continuing to dominate possession, much of Waterford's good approach play was lacking a finish as UCD defended doggedly.
Waterford skipper Kilian Cantwell came closest to leveling on 85 minutes, his crisp half-volley flashing just past Moore right-hand post.
Frustration got the better of the Suirsiders right on 90 minutes when Cantwell was sent off for a second yellow card offence.
The real drama then arrived three minutes into added time when Waterford were awarded a penalty for handball against UCD captain Jack Keaney from substitute Real Uche’s shot.
🎥 | @WaterfordFCie's Junior Quitirna hits the penalty over the bar! 😲— SSE Airtricity League (@SSEAirtricityLg) November 11, 2022
Drama in the dying seconds of the Promotion/Relegation Play-Off Final! 🤯
The full-time whistle has gone and @UCDAFC win 1-0! #LOI | #LOITV pic.twitter.com/WycxJ54ZgE
Despite missing a penalty in the First Division play-off semi-final first leg against Treaty United, Quitirna took the ball off Auoachria, who had scored from the spot in that second leg, only to blaze it high over the crossbar.
UCD: Kian Moore; Michael Gallagher, Sam Todd, Jack Keaney, Evan Osam; Sean Brennan, Evan Caffrey; Alex Nolan (Donal Higgins 83), Dara Keane, Mark Dignam; Tommy Lonergan.
Waterford: Paul Martin; Tunmise Sobowale (Raul Uche 77), Alex Baptiste, Kilian Cantwell, Darragh Power; Niall O'Keeffe; Junior Quitirna, Shane Griffin, Yassine En-Neyah (Dean Larkin 90), Phoenix Patterson; Wassim Aouachria.
Referee: Rob Harvey (Dublin)