Adrian Jarvis kicked five penalties as Harlequins claimed a surprise 15-8 victory over Bristol in the Guinness Premiership on Saturday as they continue their impressive run.
David Lemi scored the game's only try - an interception effort in the first-half - and Jason Strange added a penalty for the visitors.
The alarm bells will be ringing for Bristol boss Richard Hill, whose side might have taken advantage of a slip-up by leaders Leicester earlier in the day to return to the summit.
Without England man Shaun Perry at scrum-half, they looked short of direction and their back-row was comfortably outplayed by the outstanding trio of Andre Vos, Paul Volley and Nick Easter.
Quins may have their own problems - midfield pair Stuart Abbott and Andrew Mehrtens were missing, as was leading try-scorer David Strettle - but they were the livelier of the sides in an entertaining opening quarter.
Jarvis fired them in front with a third minute penalty, Strange leveled two minutes later and both sides moved the ball to create scoring chances.
Bristol full-back Josh Taumololo was tackled into touch a couple of metres short on the left and wing Ugo Monye went close at the other end to set up a long spell of pressure only relieved when opposite number Lee Robinson broke out.
In the end, it was an error that created the only try of the game.
Quins were attacking 10 minutes before the interval after a Mike Brown break but then threw the ball straight to Lemi and the Samoan ran 80 metres to score.
Jarvis pulled back three points with his second penalty five minutes later, when Bristol were penalised for hanging on to Tani Fuga on the ground, but he missed from in front of the posts immediately before half-time to leave his side trailing by two points.
Harlequins built up a head of steam after the break, though, and forced Bristol to concede ground and a string of penalties.
Jarvis punished them with successful shots at goal in the 52nd and 57th minutes, the latter after the visitors were reduced to 14 men when flanker Joe El Abd was sin-binned for straying offside at the breakdown once too often.
It needed an important block from Vos to deny Strange a drop-goal chance on the hour and Jarvis was able to nudge his side seven points in front with a fifth penalty 10 minutes from time.
A converted score would have given Bristol a share of the points but they were short of precision in the final minutes and unable to find a way through a defence marshaled superbly by flanker Vos and Easter.
Pens: Jarvis 5
Harlequins: 15 Mike Brown 14 Simon Keogh 13 Hal Luscombe 12 Mel Deane 11 Ugo Monye 10 Adrian Jarvis 9 Andy Gomarsall 8 Nick Easter7 Paul Volley (c) 6 Andre Vos 5 Jim Evans 4 Ollie Kohn 3 Mike Ross 2 Tani Fuga 1 Aston Croall
Replacements: 16 Jimmy Richards, 17 Ricky Nebbett, 18 Nicolas Spanghero, 19 Will Skinner, 20 Steve So'oialo, 21 Tom Williams, 22 Gavin Duffy, 23 Jordan Turner-Hall
Bristol: 15 Josh Taumalolo, 14 Lee Robinson, 13 Neil Brew, 12 Rob Higgitt, 11 David Lemi, 10 Jason Strange, 9 Brian O'Riordan, 8 Matt Salter (c), 7 Joe El Abd, 6 Nathan Budgett, 5 Gareth Llewellyn, 4 Roy Winters, 3 Darren Crompton, 2 Mark Regan, 1 Alex Clarke,
Replacements: 16 David Blaney, 17 Jason Hobson, 18 Sean Hohneck, 19 Redford Pennycook, 20 Danny Gray, 21 Sam Cox, 22 Craig Morgan
Referee: David Rose
Touch judges: Andrew Pearce, Roger Baileff
Assessor: Paul Bridgman
Television match official: Matt Peters