Is there a more raucous crowd in England than that of the Stoop? Is there a crowd more put through the mill? If only Quins were as trustworthy as their faithful, but life is never boring there.

After the craziness of the last couple of weeks, a winning try with five minutes to go might sound a little ho-hum, but having opened up a healthy lead, Marcus Smith pulling the strings wickedly, Quins did their usual of making the crowd sweat.

Glasgow turned the contest on its head by taking the lead for most of the last quarter. Only in those last minutes did Quins finally make one of their penalties to the corner yield a try from a good old-fashioned lineout and drive. And so they proceed to the quarter-finals.

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“Fans complain they are always on the edge of their seats,” said Smith. “Whenever we are ahead we let the other team in. And that is something we are trying to work on, the consistency. We are nowhere near where we want to be, but we are in another knockout game in Europe.”

The home side turned round 21-7 up, which sounds a more convincing lead than it was. All the usual Quins traits were there – a certain lack of concentration, a relishing of chaos, a steadfast refusal to take any easy points.

The madness of the win over Bath the week before, which itself came hot on the heels of the capitulation against Saracens the week before that, had the rugby world scratching its head even more than usual over the darlings of west London. And this time they were entertaining a Glasgow side packed with Scotland internationals, riding high in the United Rugby Championship.

Sure enough, the Warriors announced their threat in only the third minute, Scott Cummings burrowing over from close range after a move of 15 phases. Quins at that point looked out of joint. No Bath pyrotechnics here.

But they did have the referee. Whether a lopsided penalty count is just reward for sustained pressure or a scandalous misapplication of the laws depends mostly on the colour of your shirt, but let the record state, Quins were awarded 12 penalties in that first half to Glasgow’s two.

Their lineout-and-drive routines were less than effective at that point, failing to make anything of three penalties sent to the corner in the first quarter. When they finally scored their first try, at the start of the second, it was after another drive had broken down. So they resorted to the chaos they love. Smith’s feet were mesmeric first, then deadly precise a phase later, when he sent a kick to the corner, which André Esterhuizen touched down.

Sione Tuipulotu was shown a yellow card 10 minutes later at the concession of Glasgow’s 10th penalty of the half.

Smith danced through the compromised midfield for Quins’ second, straight from a scrum, before putting Cadan Murley away for their third on the stroke of half-time.

Last week, a 40-3 home lead was made to look less than convincing, so 21-7 did not stand a chance. As if in a script, Glasgow attacked the start of the second half as vigorously as they had the first.

This time, they scored two tries in as many minutes to level the match. A simple lineout-and-drive accounted for Johnny Matthews’ try, before the visitors tried their hand at something more sweeping, Kyle Steyn sending George Horne to the line for the equaliser.

Now it was Glasgow who enjoyed the referee’s endorsement. After a fifth consecutive penalty against Quins, Horne – glory be – chose to take the simple points. And so the Warriors had the lead again on the hour.

Matters deteriorated further for Quins when Joe Marler was shown yellow for catching a Glasgow ball-carrier in the head at the start of the third quarter. The consecutive-penalty count ballooned to nine, as Glasgow turned the screw. Just like their hosts, though, they went for the corner again and again, as if they had forgotten what easy kicks at goal can achieve. Quins held firm, finally winning their first penalty of the second half.

From that they had the foothold they needed. At the second time of asking, the umpteenth of the match, a penalty to the corner led to a convincing drive, Sam Riley claiming the try. One last defensive set was required for one last roar of the home crowd. The latter had endured enough.