The hosts scored two tries to one to claim four crucial points in a hard fought encounter.
Blair Cowan, Ian Gough and John Yapp were all outstanding making their first starts for the Club. As was Captain, George Skivington, who played the full 80 minutes.
Irish suffered an immediate set back with the loss of Kieran Low after only two minutes. The back rower sustained a rib injury and was replaced by Canadian International, Jebb Sinclair.
Brian Smith’s side regrouped after this minor disruption to kick the first points of the game after seven minutes. Karl Dickson gave away a penalty at the break down for ill discipline and Shane Geraghty made no mistake with his effort from 40 metres.
Nick Evans was awarded the chance to put his side level but uncharacteristically fluffed his straight forward effort to the left of the uprights.
He however made no mistake with his next attempt as he bisected the posts from 35 metres out. Referee, David Rose, penalised the Exiles for not being back 10 metres from a tapped penalty.
The first half continued to be a very stop start affair. Stoppages at scrum time especially took the flow out of this contest.
Geraghty kept his exemplary record with the boot up with another long range effort, however that was quickly cancelled out by a second Nick Evans penalty from in front of the sticks as Irish were pinged for being offside in defence.
With a few minutes remaining until half time London Irish were awarded a penalty which was taking quickly by Shane Geraghty. This was the most intense the contest had been up to this stage. The Exiles kept knocking at the door but were denied by resolute Quins defence.
The sides went in even at the break 6-6.
The intensity and physicality rose considerably at the start of the second half with both sides looking to play whenever possible, a stark contrast from the first.
Irish battled and finally got their reward after their pack kept the ball tight and charged over the line with Blair Cowan coming up with the ball. Geraghty added the difficult conversion to put Irish seven points clear.
Things got better for London Irish when three minutes later they had their second score. Tospy Ojo spotted Alex Lewington in acres of space and judged an inch perfect kick straight into the wingers hands. Lewington had Evans and Botica in front of him and after weaving his way in and out dived over in the corner for a great score. The try gave Irish a handy 18-6 lead.
The remaining 15 minutes saw Irish putting in a shift in defence as Harlequins threw the kitchen sink at them. Danny Care, who came onto the field with 30 minutes remaining, did his England selection no harm with a well finished try. Care scampered down the short side on the Exiles 22 and ran in to score adjacent to the posts. Evans conversion set up a tense finale.
Irish held firm and when the ball was turned over Marland Yarde booted the ball into the stands and Irish had their victory.
Irish host Caverlieri Prato at Madejski Stadium next Friday night for the first round of the Amlin Cup.
Score sequence (London Irish first): 3-0, 3-3, 6-3, 6-6, 13-6, 18-6, 18-13
Scorers: London Irish; Penalties: Geraghty (7, 31), Tries: Cowan (60), Lewington (63), Conversions: Geraghty; Harlequins; Evans (17); Tries: Care (70); Conversions: Evans
15. Topsy Ojo; 14. Marland Yarde; 13. Fergus Mulchrone (rep: Sailosi Tagicakibau, 60); 12. Eamonn Sheridan; 11. Alex Lewington; 10. Shane Geraghty (rep: Myles Dorrian, 78); 9. Tomás O’Leary (rep: Darren Allinson, 60); 1. John Yapp (rep: Matt Parr, 70); 2. David Paice; 3. Leo Halavatau (rep: Jamie Hagan, 68); 4. George Skivington (Captain); 5. Ian Gough (rep: Bryn Evans, 60); 6. Kieran Low (rep: Jebb Sinclair, 3); 7. Blair Cowan; 8. Ofisa Treviranus
Replacements: 16. Jimmy Stevens; 17. Matt Parr; 18. Jamie Hagan; 19. Bryn Evans; 20. Jebb Sinclair; 21. Sailosi Tagicakibau; 22. Myles Dorrian; 23. Darren Allinson
15. Mike Brown; 14. Sam Smith (rep: Charlie Walker, 68); 13. Matt Hopper; 12. Tom Casson (rep: Ben Botica, 26); 11. Ugo Monye; 10. Nick Evans; 9. Karl Dickson (rep: Danny Care, 49); 1. Joe Marler (rep: Mark Lambert, 54); 2. Rob Buchanan (rep: Dave Ward, 66); 3. Will Collier (rep: Kyle Sinckler, 60); 4. Nick Easter; 5. George Robson; 6. Maurie Fa’asavalu (rep: George Merrick, 70); 7. Chris Robshaw (Captain) (rep: Luke Wallace, 53); 8. Tom Guest
Replacements: 16. Dave Ward; 17. Mark Lambert; 18. Kyle Sinckler; 19. George Merrick; 20. Luke Wallace; 21. Danny Care; 22. Ben Botica; 23. Charlie Walker
Referee: David Rose