|Leinster (10) 23|
|Tries: Conan, penalty Cons: Nacewa 2 Pens: Nacewa 3|
|Cardiff Blues (9) 15|
|Pens: Patchell 5|
Leinster earned their first win of the Pro12 season but had to battle hard to beat Cardiff Blues despite dominating possession for most of the contest.
Rhys Patchell's penalties put the Blues 6-0 up but a Jack Conan try helped the home side move 10-6 up with Isa Nacewa moving beyond 400 points for Leinster.
Another Patchell penalty cut the lead to 10-9 by the break and his two further kicks put the Blues 15-13 up.
But Nacewa's third penalty and a late penalty try proved enough for Leinster.
After retaking the lead with Nacewa's 65th-minute penalty, Leinster dominated the next 12 minutes of action and the clinching penalty try came after Blues skipper Josh Navidi had been sin-binned for coming in from the side as the home side were camped on the visitors' line.
Four-times champions Leinster opened their campaign last weekend with a 16-9 defeat in Edinburgh with the Blues earning a 61-13 bonus-point win over perennial Pro12 struggles Zebre.
Patchell's two early penalties gave the Blues a 6-0 advantage at the RDS with his second effort from just inside his own half.
However, Leinster, minus their 16 Ireland World Cup squad members, regrouped to dominate possession with flanker Josh van der Flier and centre Ben Te'o both particularly prominent.
Veteran Nacewa's first penalty brought up his 400 points for the Irish province and they were ahead by the 16th minute as Conan burrowed his way over after a break by the lively Te'o.
Nacewa's conversion increased Leinster's lead but the Blues produced remarkable discipline to withstand further pressure and then snatched three points before the break as Patchell slotted another long-range penalty.
After having 76% of the first-half possession, Leinster increased their lead to 13-9 thanks to a second Nacewa penalty but the visitors continued to show great resolve as two Patchell penalties put them 15-13 up.
At that stage, a remarkable rearguard action win appeared on for the visitors but Leinster reasserted themselves in the closing 15 minutes as Nacewa's third penalty was followed by their clinching penalty try following Navidi's 75th-minute sin-binning.
Leinster were already camped on the line when the Blues skipper was yellow carded and from the resultant line-out, another maul ended up with referee Ben Whitehouse signalling the penalty try, which Nacewa converted.
Patchell attempted to snatch a losing bonus point with a late ambitious drop-goal attempt but was off target.
Leinster: Isa Nacewa (capt); Garry Ringrose, Ben Te'o, Noel Reid, Fergus McFadden; Cathal Marsh, Luke McGrath; Michael Bent, Aaron Dundon, Jamie Hagan; Ross Molony, Mike McCarthy; Dominic Ryan, Josh van der Flier, Jack Conan.
Replacements: Cian Kelleher for McFadden 61, Isaac Boss for McGrath 55, Peter Dooley for Bent 76, Bryan Byrne for Dundon 60, Royce Burke-Flynn for Hagan 48, Tadhg Beirne for McCarthy 76, Daniel Leavy for van der Flier 76
Not Used: R. Byrne.
Cardiff Blues: Dan Fish; Aled Summerhill, Tom Isaacs, Gavin Evans, Owen Jenkins; Rhys Patchell, Tavis Knoyle; Sam Hobbs, Kristian Dacey, Craig Mitchell; Jarrad Hoeata, James Down; Josh Turnbull, Josh Navidi (capt), Manoa Vosawai
Replacements: Lewis Jones for Knoyle 71, Gareth Davies for Hobbs 69, Scott Andrews for Mitchell 70, Lou Reed for Down 68, Ethan Jenkins for Vosawai 42
Not Used: Ethan Lewis, Thomas Davies, Garyn Smith.
Referee: Ben Whitehouse (WRU)
Assistant Referees: Eddie Hogan-O'Connell, Jonathan Peak (both IRFU)
Citing Commissioner: Peter Ferguson (IRFU)
TMO: Seamus Flannery (IRFU)