London Irish (3) 13
Tries: Joseph 2 Pens: Lamb
Harlequins (16) 16
Tries: Smith Cons: Evans Pens: Evans 3
Sam Smith has made a blistering start to his Harlequins career
Harlequins held off a second-half rally from London Irish to boost their hopes of reaching the LV= Cup semi-finals.
Sam Smith, 19, raced 80m to grab his second try in as many starts, with Nick Evans adding a conversion and two penalties as Quins took a 13-3 lead.
Jonathan Joseph hauled Irish back into the game with two tries but fly-half Ryan Lamb missed both conversions.
Evans kicked 11 points in total as Quins drew level on points with Pool Three leaders Cardiff Blues.
Harlequins head coach John Kingston:
"We identified from last week's debris that we had two choices.
"One was to carry on feeling sorry for ourselves and allow our season to drift by but we identified how long there was left of the season, down to the number of days, and what we can achieve is still a huge amount.
"We can only deal with what's going forward and we talked all week about this being the first day of the rest of our season and to that end it's a good start.
"I was really pleased with the defensive statement of the group."
London Irish head coach Toby Booth:
"You have to look at opportunities missed.
"Quins have obviously done quite a lot of work defensively and we tested that defence to the ultimate today and I'm sure they're very pleased. We stretched them quite considerably and they were equal to the task.
"I'm not happy with the level of finishing from the amount of possession we had but we scrummaged exceptionally well and I'm surprised we didn't get a little bit more reward."
London Irish: Hewat, Ojo, Joseph, Catt, Tagicakibau, Lamb, Richards, Murphy, Buckland, Ion, Johnson, Perry, Roche, Thorpe, Stowers.
Replacements: Lennard for Hewat (69), Rudd for Catt (69), Lalanne for Richards (63), Lahiff for Murphy (66), Coetzee for Buckland (71), Tideswell for Ion (71), Gibson for Perry (63), Garvey for Thorpe (34).
Harlequins: Brown, Lowe, Tiesi, Turner-Hall, Smith, N. Evans, Dickson, Jones, Cairns, Andress, Percival, Stevenson, York, McMillan, Guest.
Replacements: So'oialo for N. Evans (66), Croall for Jones (60), Brooker for Cairns (42), Johnston for Andress (60), Valleyos Cinalli for Percival (60), Wallace for York (60). Not Used: Clegg, Drauniniu.
Sin Bin: Turner-Hall (32), Croall (75).
Ref: Martin Fox (RFU).