Replacements: Colum Murphy, Dave Toomey, Stephen Keogh, Ferdia Doherty, Andrew Geraghty.
Replacements: Kevin Flanagan, Eddie Rossiter, Kevin Bracken, Ian Condell, Murray Kinsella.
The visitors failed to turn possession in the final third into points, despite looking lively in the opening quarter on the Aviva Stadium's back pitch.
With the rain falling heavily, both sides found the conditions difficult and handling errors prevented the players from gaining any real momentum. Lansdowne's David Hewitt and David Moroney from UL both made good breaks, but both came to nothing.
When UL scrum half Cathal Sheridan was gobbled up by the Lansdowne forwards on 13 minutes, it presented Eoghan Hickey with the chance to put the first points on the board, but he dragged his effort to the left and wide.
However, Sheridan made up for it with a wonderfully-taken try after 20 minutes when he took the ball from the back of the scrum and touched down after breaking through the covering tackle.
JJ Hanrahan, the 18-year-old Munster Academy player, added the conversion to give Bohs a lead they would not relinquish. Hanrahan was outstanding all afternoon and a vital presence for his side.
Lansdowne responded straight away. Lock Willie Earle gathered the restart and UL were penalised at ruck time. Hickey split the posts with the resulting penalty kick.
As the rain continued to pour down, Lansdowne found it hard to get into the game and they fell further behind shortly before half-time.
Hanrahan missed a penalty after 32 minutes, but UL retained the ball from Hickey's restart. When they swung the ball wide, Sheridan went down the narrow side before offloading to number 8 Sean Rennison who touched down and Hanrahan added the conversion to stretch their lead to 14-3.
The try seemed to galvanise Lansdowne into action and after recovering the restart, they mauled over the Bohs' line from outside the 22. Prop and captain John Lyne got the touchdown. Hickey's successful conversion left four points between the sides at the break.
The introduction of Leinster back rower Keogh gave Lansdowne's forwards a much-needed lift and Hickey closed the gap further with a penalty just after the resumption.
He then missed the opportunity to put Lansdowne into the lead for the first time with another penalty, five minutes later.
UL's defensive efforts was epitomised by the brilliant Dave Foley, who signed a full contract with Munster earlier this week, and Lansdowne has to resort to kicks from Hickey.
He missed another penalty after 63 minutes, but the Dubliners, who had won their three previous home games in this season's league, would have one more chance to come away with the win.
As they drove towards the line with five minutes remaining, it seemed that a try was in the offing. But Keogh's indiscretion ended their hopes. UL cleared the danger and sealed the result with a sweetly-taken drop goal from Hanrahan.
Referee: David Keane (IRFU)