Tries from Danny Care and Matt Hopper were enough for Harlequins to down rivals London Irish 26-20 at the Stoop.
Nick Evans scored four penalties for Harlequins in the first half and combined with Care's try, earned them the lead.
London Irish replied with two penalties for Shane Geraghty and a try for James Short to keep them very much in the game, with the score being 19-13 at half-time.
Harlequins secured the win in the second-half with a try for Hopper. The visitors also scored another try in the final 40 courtesy of Tom Fowlie but the home side held on.
For almost the first 30 minutes of the game, the only points came from the boots of both Evans and Geraghty respectively. Evans opened with two penalties before Geraghty kicked one of his own.
They then took it in turns, another two for the Harlequins fly-half and another one for Geraghty. Finally on 28 minutes, a great series of passes opened up a gap for Care and he sailed over the line to score the first try of the game for Harlequins.
London Irish were quick to respond when Short snatched a high ball and sped away from the Quins' defence to dive over the line and bring the score to 19-13 at the break.
Early on in the second half, a fantastic break by Jack Clifford down the middle put the Quins in a promising position and it was worked well down the wing for Hopper to score the try.
London Irish turned up the pressure on the home side when they scored on 65 minutes. Tom Fowlie raced away from the Quins' defence on the counter attack and crashed over the line but the home side held out for the remaining minutes of the game and came away with win, their first in the league since January.
Tries: Care, Hopper
Cons: Evans 2
Pens: Evans 4
For London Irish:
Tries: Short, Fowlie
Cons: Geraghty 2
Pens: Geraghty 2
Harlequins: 15 Ross Chisholm, 14 Marland Yarde, 13 Matt Hopper, 12 Harry Sloan, 11 Charlie Walker, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Luke Wallace, 6 Jack Clifford, 5 George Robson (c), 4 Charlie Matthews, 3 Matt Shields, 2 Dave Ward, 1 Mark Lambert
Replacements: 16 Rob Buchanan, 17 Darryl Marfo, 18 Seb Adeniran-Olule, 19 Netani Talei, 20 Joe Trayfoot, 21 Karl Dickson, 22 Ben Botica, 23 Ugo Monye
London Irish: 15 Andrew Fenby, 14 Alex Lewington, 13 Tom Fowlie, 12 Eamonn Sheridan, 11 James Short, 10 Shane Geraghty (c), 9 Scott Steele, 8 Tom Guest, 7 Blair Cowan, 6 Ofisa Treviranus, 5 Jebb Sinclair, 4 Nic Rouse, 3 Halani Aulika, 2 David Paice, 1 Tom Court
Replacements: 16 Jimmy Stevens, 17 Matt Parr, 18 Leo Halavatau, 19 Sean Cox, 20 Luke Narraway, 21 Darren Allinson, 22 Chris Noakes, 23 Eoin Griffin
Date: Saturday, 7 March
Venue: Twickenham Stoop
Kick-off: 15:00 GMT
Referee: JP Doyle
Assistant Referees: Wayne Barnes & Luke Pearce
TMO: Stuart Terheege