Replacements: Leo Auva'a, Vinny Soden, Brian Coyle, Fergal Lawlor, James Kearns.
Replacements: Rory Harrison, Risteard Byrne, Donagh Lawler, Luke McGrath, James Thornton.
Two second half penalties from goal-kicking winger Josh Glynn after 57 and 66 minutes made certain of the result.
UCD, who put 55 points on Dolphin last Sunday, had a 17th minute try from lock Emmet MacMahon, but could only add a penalty through Niall Earls over the remaining hour.
Old Belvedere had to do it the hard way after losing talismanic captain Daniel Riordan to an early injury. James Kearns replaced him and drew praise from the management afterwards for his assured performance.
The home side were gunning for revenge after UCD beat them 33-26 at Belfield in October, and they hit the front here in the eighth minute.
A brilliant solo try from O'Dwyer did the trick, the lively winger showing his pace to break from his own half and outstrip the UCD cover to run in an unconverted effort.
Towards the end of the first quarter, the students levelled matters at 5-5 thanks to MacMahon's score and they then recovered well from the concession of a second try to Conan.
Earls' penalty cut the gap to 10-8 five minutes before the break, but 'Belvo crucially managed to extend their lead to five points with Glynn's first penalty of the afternoon.
The weather conditions were particularly testing at times, especially during a hailstorm, and UCD never really got an opportunity to get the best out of their highly regarded back-line that included underage international Billy Dardis at full-back.
Although the visitors made a strong start to the second half, Old Belvedere were able to keep them out - showing the form which has made them the division's third best defensive unit to date.
UCD then had Connacht recruit Conor Gilsenan yellow carded and 'Belvo wasted no time in widening the margin with Glynn landing two killer blows off the kicking tee.
The left winger, who tallied up 19 points against Young Munster last weekend, converted two penalties entering the final quarter.
UCD could not muster a response and in a further boost to 'Belvo's title hopes, the early indications are that ful-back Riordan will be fit to lead the team in the top of the table clash next Friday.
Old Belvedere head coach Paul Cunningham told the Irish Independent: "It will be massively tough at Castle Avenue (on Friday), but we're looking forward to the challenge. We will be looking to show the same attitude we displayed in beating UCD.
"That was a great win given that we lost Danny (Riordan), our best player all year, in the opening few minutes.
"We tackled everything that moved and (replacement) James Kearns did a great job after coming on for Danny."
Referee: Dudley Phillips (IRFU)