Ireland players Harry Byrne and Gus McCarthy both suffered head injuries as Leinster's 11-match winning run came to an end at the Cardiff Arms Park.
Out-half Byrne had been released from Ireland's Six Nations camp to get some game time but required a head injury assessment after a tackle attempt in the third minute and did not return to the action.
The 26-year-old had not featured for Andy Farrell's side so far in the championship but would have been in the running to make the matchday squad for Friday's round-four clash against Wales at Aviva Stadium.
Hooker McCarthy, alongside back Jimmy O'Brien also released from international camp, came on as a replacement for John McKee at the end of the first half but was removed with six minutes to play when his gumshield alert was triggered after a tackle.
However, centre Robbie Henshaw, playing his first game since suffering a knee injury against Bayonne in mid-January, appeared to come through unscathed and should be available for Farrell's consideration.
The first half was devoid of any major incidents as the teams struggled in a heavy downfall in the Welsh capital.
But the hosts were able to take the lead through a Callum Sheedy penalty when Charlie Tector, who had just replaced Byrne, was in the bin for an earlier dangerous tackle.
Cardiff grabbed the first try of the game in the 54th minute when Mason Grady and Dan Thomas broke downfield before passing to Davies, who raced in for an unconverted score.
Soon after Cardiff were reduced to 14 when Jacob Beetham was yellow-carded, Henshaw helped to set up replacement Luke McGrath's try as he combined with Andrew Osborne in midfield to send the scrum-half free to run in under the posts with Tector converting in the 67th minute.
But Leinster, missing the majority of their frontline Ireland contingent, were unable to work another chance as Corniel van Zyl's team recorded just a second win in 19 years against the Irish side, who missed out on a chance to move top of the table.
