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
Cardiff 15-33 Harlequins
Ben Thomas launches a counter attack. Cardiff are racing up field and Mason Grady trundles down the left touchline through tackles.
Quins eventually get the big lad out... but it's better from the home side.
Have Harlequins stepped off the gas here?
Cardiff 15-33 Harlequins
Harry Millard chips ahead but the bounce of the ball lands in Alex Dombrandt's big hands.
Cardiff are not getting the bounce tonight.
Cardiff 15-33 Harlequins
Thomas Young's return from injury is over. Two tries... not a bad night's work after six weeks out with a calf problem.
Local lad Mackenzie Martin is on.
Lock Teddy Williams makes way for Rory Thornton.
Image source, Huw Evans Picture AgencyCardiff 15-33 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
Very frustrating passage of play there from Cardiff, they didn't have enough options.
Tinus de Beer was isolated and all he can see is a blanket of Harlequins fans, he needs his forwards coming off his shoulder.
At this moment in time Harlequins are just sucking up everything Cardiff have to offer.
Cardiff 15-33 Harlequins
Cardiff enjoying a rare spell of posesion here but not going very far.
And then Grady coughs up a high ball.
Sums up their night.
Cardiff 15-33 Harlequins
Mason Grady takes the ball at a standstill and is dumped onto his backside.
Cardiff need to get him much better ball than that because he can be so dangerous.
Cardiff 15-33 Harlequins
Harlequins have been ruthless.
In the space of ten minutes either side of half-time they have turned 14-15 into 33-15.
Devastating.
Cardiff 15-33 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
Marcus Smith is having a sublime night this evening, 150 games for Harlequins and he's pulling the strings tonight.
It all comes from Cardiff ill-discipline and now Harlequins are turning the cogs and picking up the momentum.
Cardiff 15-33 Harlequins
Wales prop Corey Domachowski is on for Rhys Carre.
Marcus Smith
Smith squeezes over for Quins' fifth try.
He punches the air... oh he's really enjoying his 150th appearance for the club.
Cardiff did a decent job holding the initial drive but quick ball, the vision of Danny Care and Smith was loitering with intent in the left corner.
Image source, Huw Evans Picture AgencyCardiff 15-28 Harlequins
And another penalty for Quins and Marcus Smith boots them towards the corner.
Ominous.
Cardiff 15-28 Harlequins
Quins scrum wins a penalty.
The Quins pack are coached by former Cardiff prop Adam Jones who knows a thing or two about scrums!
Cardiff 15-28 Harlequins
Cardiff hooker Liam Belcher is also off. He was struggling with a wrist injury in the first half. Youngster Efan Daniel gets 40 minutes.
Cardiff 15-28 Harlequins
Joe Launchbury has not emerged for the second half, Irne Herbst is on.
Cardiff 15-28 Harlequins
Tinus De Beer gets the second half underway.
More of the same please lads.
HT: Cardiff 15-28 Harlequins
Image source, Huw Evans Picture AgencyAndre Esterhuizen is tackled by Liam Belcher
Image source, Huw Evans Picture AgencyJames Botham goes on the charge
Image source, Huw Evans Picture AgencyTinus de Beer brings down Alex Dombrandt
Image source, Getty ImagesDanny Care gets the ball away for Harlequins
Image source, Getty ImagesCardiff Arm's Park paid tribute to the late great JPR Williams with a minute's applause
Here's the scores from today's Investec Champions Cup action
POOL 1
Lyon 34-20 Connacht
Bristol 17-31 Bulls
POOL 2
Cardiff 15-28 Harlequins (half-time)
Ulster 10-22 Toulouse (half-time)
POOL 3
Exeter Chiefs 19-17 Glasgow Warriors
Toulon 18-29 Munster
POOL 4
Leinster 43-7 Stade Francais
Stormers 31-24 Sale
HT: Cardiff 15-28 Harlequins
To pick up on Dafydd's point, only Damien Penaud had beaten more defenders in the Champions Cup this season than Marcus Smith.
His four conversions have also taken him to 28 points in the competition this season - third overall and the top English scorer.
Image source, Rex FeaturesHT: Cardiff 15-28 Harlequins
Dafydd James
Former Lions and Wales back on BBC Radio Wales
It's been a fantastic first half, end to end stuff. We've had tries, we've had controversy, it's been fantastic.
Exactly what the crowd wanted, some are booing, but I think it's a great spectacle.
Fantastic passages of play, the majestic Marcus Smith running from his own tryline but Cardiff will be ruing the opportunities they have had.
I've been particularly impressed by Thomas Young's workrate.
Cardiff 15-28 Harlequins
And the whistle goes to bring an end to a thrilling half of rugby.
The players will need every second of the half-time break to get their breath back.
Six tries already, a bonus point for Harlequins and a brace for Thomas Young.
Can't help feel that last try for Quins could be decisive.