Despite the red card, the visitors continued to be the better side with Cardiff having to survive sustained late pressure in order to pick up two points and cement third position in the league.
Munster returned to winning ways at a rain-lashed Virgin Media Park by beating Ospreys 23-0 in a repeat of last season’s BKT United Rugby Championship quarter-finals.
Cardiff were in contention throughout but two tries from international prop Nicky Smith and others from Justin Tipuric and Luke Morgan proved just enough.
Jordan Larmour scored his first senior hat-trick for Leinster as the Irish province produced a second-half masterclass to hammer Ospreys 61-14 at the RDS.
The Ospreys’ unbeaten record against South African opposition in the United Rugby Championship came to an end with a 61-24 defeat by the Bulls.
Gloucester fly-half Adam Hastings is set to make his return from injury on Friday against the Ospreys in the Challenge Cup quarter-final at Kingsholm.
They can no longer afford big-ticket imports but an emerging crop of talented youngsters gives Ospreys cause for optimism.
Benetton produced a late scoring burst to defeat United Rugby Championship opponents the Ospreys 18-13 at Stadio di Monigo.