Harlequins knockout hopes still alive when they host Ulster next week
Cardiff exit the Champions Cup with a game to spare
England fly-half Marcus Smith scores on his 150th Harlequins appearance
Harlequins prop Dillon Lewis scores against his former team
Thomas Young crosses twice on his Cardiff return
FT: Cardiff 15-52 Harlequins
So that's it for our coverage of what has been an epic day of European Champions Cup rugby.
Lyon, Exeter Chiefs, Bulls, Munster, Leinster, Stormers, Toulouse and Harlequins all claimed wins and a step closer to the final at Tottenham Hotspur Stadium in May.
Join us next week for the final round of pool matches when qualification for the knock-out stages will be decided.
FT: Cardiff 15-54 Harlequins
Harlequins scrum half and player of the game Danny Care on S4C:
"I don't think I deserved man of the match, some of the forwards were superb and the backs too but they've given it to the old man.
"It was a great win, I love coming here in front of a packed Cardiff stadium. Cardiff played some brilliant stuff but we're chuffed with the five points."
Image source, Getty ImagesFT: Cardiff 15-54 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
It was a sublime performance from start to finish from Harlequins.
There was a turning point with Oscar Beard's try which I believe shouldn't have been a try.
Cardiff didn't kick on in the second half and Harlequins were much the better team on the night.
FT: Cardiff 15-52 Harlequins
Pool Two leaders Toulouse have booked their place in the next round with a 48-24 win at Ulster in Belfast.
Harlequins are now level on 10 points with Bath, who face Racing 92 tomorrow.
Quins welcome Ulster next week for what could be a decider.
Cardiff, with two points and three defeats, are virtually out of the Champions Cup baring a miracle set of results.
But they could yet progress to the last 16 of the Challenge Cup if they win at Racing 92 next week.
FT: Cardiff 15-54 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
Cardiff capitulated in the end, a speculative kick which bounced back up on the 4G pitch over Rey Lee-Lo and then Tyrone Green who's been sublime all evening gets on the end of it.
Cardiff 15-47 Harlequins
And that's it. Marcus Smith's conversion is the final kick of the game.
Tyrone Green try, Marcus Smith con
Well he deserves that.
Tinus de Beer puts in a speculative chip but the bounce eludes the attackers.
Oscar Beard gathers before releasing the full-back who streaks through from 40 yards out and dives between the posts.
What a way to finish an emphatic performance.
Image source, Getty ImagesCardiff 15-47 Harlequins
Harlequins pack has done a number on Cardiff tonight.
Their forwards have dominated almost every area. Maybe the breakdown has been more level.
But the Quins pack have given Danny Care and Marcus Smith an armchair ride.
Cardiff 15-47 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
That was a catalogue of errors the last pass went to ground.
Cardiff have made a lot of mistakes but now it's just wave after wave of Harlequins forwards crossing the gainline.
It's a dejected Cardiff team coming back up to the halfway line, they want the time to run out.
Fin Baxter try, Marcus Smith con
Again Harlequins go through the phases, a series of pick and goes edges closer to the line and a tiring Cardiff defence eventually cracks.
That's seven.
Cardiff 15-40 Harlequins
Attendance has been confirmed as a 12,000 sell-out.
It's the one silver-lining to tonight for Cardiff who are heading out of the Champions Cup as it stands.
Cardiff 15-40 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
What a vintage performance this has been from Marcus Smith, I think he's only missed one kick.
Cardiff will be really disappointed after the way they started the first half but it's all about saving face for them now here.
Cardiff 15-40 Harlequins
Cardiff scrum-half Tomos Williams makes way for Ellis Bevan.
Quins hooker Nathan Jibulu replaces Jack Walker.
Centre Lennox Anyanwu also on for last nine minutes.
Cardiff 15-40 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
That's the final nail in the coffin there as Dillon Lewis dives over. Will Porter was sublime there, the catalyst down the right flank, drawing playing in, not dying with the ball.
Then Marcus Smith, using his forwards such as Alex Dombrandt, before Dillon Lewis goes over much to Cardiff's disappointment.
Dillon Lewis try, Marcus Smith con
It had to come eventually... and it had to be a former Cardiff player!
Dillon Lewis crashes over from close range... and gets a high-five from set-piece coach Adam Jones, but boos from the Arms Park faithful.
Smith adds the conversion from out wide to bring up 40 points.
Image source, Huw Evans Picture AgencyCardiff 15-33 Harlequins
Cardiff getting a lot of tackle practice here as Quins go through the phases.
Tyrone Green and Will Porter breaking through.
Cardiff 15-33 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
The Harlequins front five have dominated Cardiff and the back row have been immense with James Chisholm and Alex Dombrandt getting around the park.
It's giving Marcus Smith an armchair ride.
Cardiff 15-33 Harlequins
Danny Care's night is over, another top performance from the scrum-half. Will Porter gets about 20 minutes.
As does former Cardiff prop Dillon Lewis who knows all about this ground after leaving just last summer.
Owen Lane is on for the home side for Willis Halaholo.
Cardiff 15-33 Harlequins
Wow... we've had 15 minutes without a score. What's going on?
Cardiff 15-33 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
That's what Cardiff needed, Tomos Williams taking the tap quickly, causing problems for the Harlequins defence.
It's a wonderful tackle from Marcus Smith on Mason Grady.
You need to give Grady more of the ball, he's too isolated on the wing, I would bring him into midfield.