The Blues ended years of miserable failure in cross-border tournaments when they became the first Welsh side to qualify for next March's semi-finals of the EDF Energy Cup, markedly the best team in what was a distinctly average Group B.
Irish's route to the semi-finals lay in beating the Blues and not conceding a bonus point but, even though they took an early lead when the veteran wing Justin Bishop finished off a counter-attack by the scrum-half Richie Rees, they arrived in Wales in body rather than spirit.
The Blues dominated from the off, aided by a welter of penalties. In truth a cross-border tournament of any significance should have neutral referees, not to stifle potential bias but to deny the home side the advantage of being familiar with law interpretations, not least at the breakdown.
After the Blues had been denied an opening try when Mark Stcherbina's pass to Mosese Luveitasau following a lineout steal was a shade forward, three penalties from Ben Blair extinguished Irish's lead and the game started to become fractious as the visitors grew frustrated.
The Irish captain, Bob Casey, complained to the referee that sections of the crowd were verbally abusing his players, but they must have faced a volley from their head coach Brian Smith at the interval after leaking two tries at the end of the opening half.
The flanker Martyn Williams scored the first as the Blues built momentum from three successive penalties while the second, finished off by Chris Czekaj, had an element of slapstick about it with Irish messing up another of their lineouts and allowing the wing to find space where none should have existed.
Czekaj chipped the ball over the tryline, where the covering wing Sailosi Tagicakibau only had to touch it down for a drop-out, but he somehow contrived to miss it. Czekaj duly made it 21-7.
Irish bent their backs a bit more in the second period when the introduction of the second row Nick Kennedy saw their lineout improve - it could hardly get any worse as Irish had lost that set-piece 14-2 in the first half - and they tried some fancy passing moves, with mixed success as the rain started to fall.
Their centres Seilala Mapusua and Dominic Feaunati were more comfortable seeking contact than employing quick hands and feet, but they had a go, as the rest of the Premiership clubs will have to if England are to gain redemption, but Czekaj's second try of the night with the game's final move sealed a routine victory for the Welsh region.
Teams
Cardiff Blues: Blair; Luveitasau, J Robinson (MacLeod, 74), Stcherbina (Shanklin, 64), Czekaj; N Robinson, Phillips (Evans, 79); Jenkins (Yapp, 75), Thomas, Filise, Jones, Goode (Davies, 70), Morgan, Williams (Lewis, 79), Rush (capt).
Tries: Czekaj 2, Williams. Cons Blair 2. Pens Blair 4.
London Irish: D Armitage; Bishop (Horak, 80), Feaunati, Mapusua, Tagicakibau; Geraghty (Everitt, 60), Rees (Hodgson, 68); Collins (Fitter, h-t), Paice, Lea'aetoa, Hudson (Kennedy, 45), Casey (capt), McCullen, S Armitage, Leguizamon (Murphy, 64).
Try: Bishop. Con Geraghty.
Sin-bin: Mapusua, 73
Hill back with a bang
The England flanker Richard Hill scored a try for Saracens on his return from a 16-month injury lay-off as the defending champions Wasps were eliminated from the EDF Cup after a 26-15 defeat in Group B. The 33-year-old Hill, who suffered a serious knee injury in the first Lions Test in New Zealand, defied teeming rain to put in an all-action display.
Hill's early second-half try helped turn the match after Wasps had dominated to lead 10-6 at the break. Both clubs fielded weakened teams, Wasps giving a debut to Tom French.
