Cardiff named eight Taulupe Faletau in their starting line-up on Thursday afternoon, although boss Corniel van Zyl admitted the Wales number eight still had a few boxes to tick because of niggles.
The Blue and Blacks opted against fielding the 35-year-old for the first time since a shoulder injury suffered at Sharks in March.
In-form Taine Basham was a late inclusion and continued his strong start to the season as his side’s most dynamic carrier.
Cardiff travel to free-flowing Northampton in the Champions Cup on Sunday, 18 October (17:30 BST).
With a five-day turnaround from that fixture to a home URC game against Sharks, they must choose the right time to reintegrate Faletau.
Leinster: Keenan; Kenny, Ringrose, Osborne, J O’Brien; Prendergast, Coffey, Usanov, Sheehan (capt), Furlong, McCarthy, Ryan, Deegan, Penny, Conan.
Replacements: Kelleher, Dooley, Clarkson, Spicer, Ericson, Gunne, Gabriel, Henshaw.
Cardiff: Young; Beetham, Millard, Malan, Grady; Sheedy, Davies; Southworth, Belcher (capt), Sebastian, McNally, T Williams, Mann, Thomas, Faletau.
Replacements: E Lloyd, Barratt, Wainwright, Nott, Paea, Mulder, J Evans, S Emanuel.
Yellow: Aled Davies 16.
Referee: Sam Grove-White (Scotland)
Assistant referees: Keane Davison (Ireland), Jonathan Erskine (Ireland)
TMO: Andrew McMenemy (Scotland)