CELTIC LEAGUE: Sunday, March 20Connacht 21 Leinster 26, The SportsgroundScorers: Connacht: Tries: Matt Lacey, Bernard Jackman; Con: Eric Elwood; Pens: Elwood 2, Mark McHughLeinster: Tries: Felipe Contepomi, Victor Costello; Cons: David Holwell 2; Pens: Holwell 4
Declan Kidney's men are up to third in the table ahead of Good Friday's Lansdowne Road clash with the Scarlets, following their second win over the westerners this season.
Former Ireland international Costello scored a trademark touch down as he struck off the base of the scrum in what proved to be Leinster's final score.
The visitors - losers in three of their last four league outings - held on thanks to a 19-6 half-time lead and despite the late sin-binning of lock Des Dillon.
And if Costello was pleased with only his second league try in three seasons - back row colleague Keith Gleeson should be even more.
He came through his first 80 minutes for Leinster since breaking his ankle last August and on a windy afternoon, captained the men in blue to victory.
Felipe Contepomi's 30th-minute intercept try paved the way for a 13-point interval lead for Gleeson and co.
Two opening penalties from Kiwi David Holwell got Leinster off the mark before Connacht veteran Eric Elwood replied with a dead centre shot.
Holwell - who kicked 16 points in all - swapped another with Elwood and watched gleefully as Puma powerhouse Contepomi robbed Elwood's intended slip for Paul Neville to race to the posts.
Elwood cancelled out a Holwell injury-time penalty on the restart but could do little about Costello's barge over.
Connacht flanker Matt Lacey made a fight of it in the end - as he powered over in the left corner on the hour-mark and while Elwood converted substitute Bernard Jackman's close range drive on 78 minutes but it proved too little, too late for Michael Bradley's side as they remain without a home win in the league since November.
The Sale Sharks - Jackman's former club - are next in Galway for the westerners' Challenge Cup semi-final first leg on Saturday, April 2 - before league leaders the Ospreys visit eight days later.
(15) Matt Mostyn(14) Conor McPhillips(13) Darren Yapp(12) Mark McHugh(11) David Slemen(10) Eric Elwood(9) Chris Keane(1) Ray Hogan(2) John Fogarty(3) Stephen Knoop
Replacements used: Mick Carroll for Neville (60 mins), Bernard Jackman for Fogarty (62), Dan McFarland for Hogan (66), Mike Walls for Keane (72). Not used: Peter Bracken, Justin Meagher, Ted Robinson.
(15) David McAllister(14) John McWeeney(13) Gary Brown(12) Felipe Contepomi(11) David Quinlan(10) David Holwell(9) Brian O'Riordan(1) John Lyne(2) David Blaney(3) Ricky Nebbett(4) Ben Gissing(5) Des Dillon(6) Ciaran Potts(7) Keith Gleeson (Capt)(8) Victor Costello
Replacements used: Leo Cullen for Gissing (61 mins), Jamie Heaslip for Costello (61), Brian O'Mearafor O'Riordan (63), Gavin Hickie for Blaney (65). Not used: Niall Treston, Aidan McCullen, John Hearty.
Sin-bin: Des Dillon (Leinster) (78 mins)HT: Connacht 6 Leinster 19; Attendance: 1,100Referee: Nigel Williams (Wales)