Sam Smith scored a brace of tries with Nick Easter, Matt Hopper, Rob Buchanan and Ben Botica also among the scorers for Connor O'Shea's high fliers, who even managed two penalty tries at scrum time.

The most Zebre could manage on a bitterly cold day was a first-half breakaway try from Leonardo Sarto and a late consolation for Alberto Chillon.

With Biarritz Olympique losing to Connacht the night before, Quins' destiny now lies very much in their own hands, and victory in next week's return fixture against the same opposition at the Twickenham Stoop will effectively seal their passage through to the quarter-finals - with a home tie in the last eight their target.

Harlequins barely had to break sweat for some of their tries, the first of which came for livewire Smith on 26 minutes, a routine dash for the corner after the Zebre defence had been stretched on the back of a Maurie Fa'asavalu turnover.

Things went from bad to worse for the Italians when Mauro Bergamasco was sent to the bin shortly after for a ruck offence.

And on the pitch it was pretty much one-way traffic as Quins put themselves in total command of the group with three down and three to go.