Piet van Zyl scored two tries as an excellent all-round display from London Irish gave them a 35-5 victory over Harlequins at the Stoop - just their third win of Aviva Premiership season.
The visitors thought they had their first points in the fourth minute, but Alex Lewington's effort was chalked off after referee Ian Tempest adjudged James Marshall's final pass to have been forward.
Irish eventually did get the first points, with Tom Fowlie bursting through the hosts defence before offloading to Van Zyl to finish off.
They doubled their lead less than 10 minutes later, Marshall's cross kick was collected by Lewington and his kick over Mike Brown bounced its way into Van Zyl's hands for his second.
Quins had a great chance to close the gap minutes later, but scrum-half Danny Care's knock on from the back of a five-metre scrum ensured the gap stayed at 14.
The visitors extended their lead even further when Max Northcote-Green finished off a move in the corner after some excellent build up play by the Irish backs.
A Tommy Bell penalty on the strokes of half-time saw the Premiership's basement club take a well-deserved 22-0 lead into the break.
And the visitors extended their advantage with the first points of the second half, Bell once again slotting a penalty through the uprights.
Harlequins did eventually get on the scoreboard through Jack Clifford, the flanker diving on Care's chip into the corner, but only after the TMO had had a long look at the grounding.
That try could have been the catalyst for a comeback, but more sloppy passes constantly stopped them gaining any kind of momentum.
The visitors on the other hand, seemed a lot more composed and disciplined in their play, epitomised by their fourth try.
Centre Fowlie touched down Van Zyl's inch perfect chip into the back of the in-goal area to put the game out of sight of Harlequins.
The try itself only came about after Care was sent to the sin bin for failing to retreat 10 yards, yet another sign that the hosts were not quite at the races.
Another penalty by Bell soon after pushed London Irish's lead to 30 points.
Despite being down to 14 men for the last 10 minutes following Charlie Matthew's sin bin, the hosts had a chance to get a consolation try, but Chris Robshaw dropped the ball with the line at his mercy.