Glasgow pile forward again and make their way into the Quins 22 again.

Well over 20 phases as they probe for a potentially decisive fourth try.

There was a lot of chat in the first half about Glasgow's discipline, but Quins have conceded six penalties in the second period to Glasgow's none.

A complete reversal.

There's a debate as to what colour the card should be, but the TMO and referee decide there's enough mitigation to make it yellow rather than red.

Image source, PA Media

The officials are checking a tackle from Joe Marler on Rory Darge.

There's definite contact with the Scotland flanker's head - Marler could be in trouble here.

George Horne continues his perfect record off the tee this evening, and gives Glasgow the lead once more.

The visitors have now scored 17 unanswered points since the break.

Zander Fagerson steps off his left foot and suddenly has open ground in front of him.

The Scotland prop looks like a man that doesn't often find himself in that position and steps into contact when he could have probably gone for the line.

Harlequins are then called for offside, and George Horne calls for his kicking tee.

Harlequins full-back Tyrone Green gets caught in two minds under a high ball, and only succeeds in throwing the ball out for a Glasgow lineout.

Suddenly everything is going Glasgow's way.

Joe Launchbury is on for Quins, and his first lineout ends with a Glasgow penalty.

Tom Jordan kicks Glasgow back towards the home 22.

Peter Wright
Former Scotland prop on Sportsound

That's quality.

All the players are involved. Jamie Dobie's dummy allows Kyle Steyn to loop round, and George Horne does what all good scrum-halves do to get there in support.

Danny Care flies out of the line and smashes Tom Jordan with a fairly high shot.

Quins are then pinged at the breakdown, and Tom Jordan kicks to the corner.

Glasgow win a penalty at the lineout and kick to the corner.

The ball goes loose, but as Quins look to clear, they throw a forward pass that gifts Glasgow another opportunity.

Quins rush up in defence, and Josh McKay goes for a glory pass out to Jamie Dobie, who came on in the first half when Kyle Rowe went for an HIA.

However, there's too much on it and it bobbles into touch.

Kyle Steyn puts boot to ball after Andre Esterhuizen knocks-on in midfield.

Steyn and Josh McKay both hare after the ball, but Cadan Murley gets back well to ground the ball in-goal.

Glasgow have a scrum 5m out though - a big chance to hit back early in this second half.

Away we go again...

The players are back out in London.

Joe Marler is on for the hosts, while Sione Tuipulotu has served his 10 minutes in the bin and Glasgow are back up to their full contingent.

A reminder that the winners tonight will face Bordeaux Begles or Saracens in the quarter-finals.

As well as getting back in the referee's good books, Glasgow need to find a way to get a grip of Marcus Smith after the break.

The England fly-half became increasingly influential as the first half wore on, setting up two tries and scoring one himself.

Image source, PA Media

Meanwhile it's half-time in the Challenge Cup at Kingsholm, where Gloucester lead Castres 21-10 thanks to tries from Zach Mercer, Johnny May and Max Llewellyn.