Ian Madigan kicked 13 points Leinster as took advantage of leaders Munster's defeat at the Scarlets with a thrilling 28-25 win over Glasgow.
Returning to the RDS, where they lost to Leinster in last year's semi-finals, Glasgow gave their all in pursuit of only their second victory in 18 visits to Dublin.
Madigan accumulated 11 points and Noel Reid and man-of-the-match Darragh Fanning broke through for tries as Leinster took a 21-15 lead into half-time.
Glasgow showed their attacking capabilities, with two Richie Vernon tries and an injury-time penalty from Finn Russell making it a six-point difference.
Niko Matawalu burrowed over from a ruck for the Warriors' third try with Russell's conversion putting them a point clear after 51 minutes.
But Leinster's pack eventually broke the Scots' resistance, flanker Ruddock muscling over for the decisive seven-pointer on a wet night in the Irish capital.
Leinster hit the front in the sixth minute, Sean Cronin offloading out of a midfield tackle for Reid to dart into space and he broke Peter Murchie's tackle to raid in beside the posts.
Madigan converted but Glasgow were back level by the 12th minute as Vernon touched down after being fed by Ruaridh Jackson, who took advantage of Jack McGrath's missed tackle.
Russell's successful kick tied things up at 7-7 before Leinster retook the lead by the end of the first quarter thanks to a Madigan penalty.
But a Warriors try from only their second visit to the hosts' 22 stung O'Connor's side, who were made pay for some sloppy defending.
Tommy Seymour tested the Leinster rearguard out wide before the Scottish outfit recycled swiftly for big centre Vernon to barge over to the right of the posts. Russell failed to convert this time.
Leinster used their forwards to steady the ship, with the accurate Madigan knocking home two penalties to make it 16-10.
The Irish province sensed a try before the interval and, after Ruddock went close from a maul effort and Eoin Reddan was stopped short, slick hands from Madigan and Zane Kirchner released winger Fanning for a simple finish in the right corner.
Madigan's conversion attempt fell narrowly wide to the left and the Warriors squeezed in a late three-pointer from Russell, who punished Jordi Murphy for going offside.
Josh Strauss bulldozed his way through the Leinster defence to give Glasgow the first sniff of a try in the second half, and television match official Alan Rogan confirmed the grounding by Matawalu from a close-in ruck.
Russell's kick made it 22-21 to the visitors as they looked for a repeat of their 2011 win here.
Again, though, Leinster's durable forwards grew in influence as, following 12 power-packed phases of carrying in the Scots' 22, Ruddock managed to stretch over in the right corner.
Madigan topped off the try with a fine kick from the right and, although Glasgow responded with a late Russell penalty for a losing bonus point, Leinster wore down the clock with a strength-sapping 22 phases under Isaac Boss' baton.