Harlequins are on the brink of an Investec Champions Cup knockout place after a bonus-point, eight-try hammering of Cardiff.

In contrast, Cardiff are facing Champions Cup elimination.

Home flanker Thomas Young scored two tries in an outstanding display.

Young’s performance was especially impressive as he was playing his first game since suffering a calf injury suffered in November.

It was another Arms Park thriller played in front of a capacity crowd of 12,000 for a second consecutive fixture after the ground was sold out for Cardiff’s victory against Dragons in the United Rugby Championship (URC) on 26 December.

There was almost a capacity crowd in Cardiff’s European defeat against Bath in December 2023 with both Anglo-Welsh occasions fuelling the desire of those fans who want the two nations to combine in a league format.

For all the attacking endeavour and entertainment, there was a noticeable gulf in class between the two sides with Harlequins currently second in the Gallagher Premiership and scrum-half Danny Care dictating matters.

It was a chastening night for Cardiff, who have lost all three European matches after previous defeats against Bath and Toulouse and lie bottom of Pool 2.

Matt Sherratt’s side finish their campaign against Racing 92 in Paris next Saturday hoping to finish fifth out of six in their group, which could lead to dropping down into the second-tier European Challenge Cup.

Harlequins, who followed up the victory against Racing 92 in Paris, but have also been thrashed by Toulouse, finish their pool stage at home against Ulster next weekend.

Fast start

Young was one of five Cardiff personnel changes with flanker Alex Mann prop Rhys Carre, centre Willis Halaholo and wing Harri Millard starting, but Wales wing Josh Adams was still missing with a leg injury.

Lewis was among the Harlequins replacements, but another old Arms Park favourite Jarrod Evans was injured.

Links between the two clubs also included Harlequins coaching staff members Danny Wilson, Billy Millard and Adam Jones, who all former coaches or players at Cardiff.

Smith, 24, led his side out on his 150th Harlequins appearance, but the English club were missing injured prop Joe Marler.

There was a moment of applause to mark the death of former Wales and British and Irish Lions full-back JPR Williams before Cardiff opened the scoring with a Tinus de Beer penalty.

Cardiff produced an ingenious first try as they isolated Care with a clever de Beer chip kick which was collected by towering lock Seb Davies before he released the rampaging Young.

An off-the-ball altercation between Young and James Chisholm ensued after sloppy restart work from the hosts before Harlequins responded with a try from hooker Walker from a flawless driving line-out. Smith converted.

Full-back Cam Winnett was forced off the field for a head injury assessment (HIA) and replaced by Ben Thomas. Winnett passed his HIA, but stayed off because he had picked up another injury.

The alteration failed to disrupt the home side as Young gained his second try with Millard involved twice, giving the final pass which was not deemed forward.

Scrum-half Tomos Williams, who has announced he is leaving for Gloucester next season, was also heavily involved. De Beer, outstanding in defence, converted from the touchline.

Harlequins again responded with a well-worked try which ended with centre Esterhuizen powering down the left hand side.

Smith converted before brilliantly launching a counter-attack from his own line which almost ended in a try.

A superb high catch from full-back Green set the platform for flanker Evans to power over for the visitors’ third converted try.

Centre Beard gained the bonus point try as he scythed through the Cardiff defence with a desperate cover tackle from Mason Grady failing to deny the score after multiple television replays were investigated.

Smith converted to give Harlequins a 28-15 half-time lead in an opening 40 minutes which produced six tries.

Captain Liam Belcher had been struggling in the first half with injury and was replaced by Efan Daniel before Harlequins continued where they left off with Smith grabbing the fifth try.

There were pantomime boos for Lewis who scored against his old side and replacement prop Baxter demonstrated the power of the visitors before full-back Green completed the rout.

Cardiff: Cam Winnett; Harri Millard, Rey Lee-Lo, Willis Halaholo, Mason Grady; Tinus de Beer, Tomos Williams; Rhys Carre, Liam Belcher (capt), Keiron Assiratti, Teddy Williams, Seb Davies, Alex Mann, Thomas Young, James Botham.

Replacements: Efan Daniel, Corey Domachowski, Rhys Litterick, Rory Thornton, Mackenzie Martin, Ellis Bevan, Ben Thomas, Owen Lane.

Harlequins: Tyrone Green; Nick David, Oscar Beard, Andre Esterhuizen, Cameron Anderson; Marcus Smith, Danny Care; Fin Baxter, Jack Walker, Will Collier, Joe Launchbury, George Hammond, James Chisholm, Will Evans, Alex Dombrandt (capt).

Replacements: Nathan Jibulu, Jordan Els, Dillon Lewis, Irne Herbst, Chandler Cunningham-South, Will Porter, Lennox Anyanwu, Louis Lynagh.

Referee: Frank Murphy (Ireland)

Assistant referees: Peter Martin (Ireland) & Sam Holt (Ireland)

TMO: Joy Neville (Ireland)