Exeter remained on course for the Premiership title play-offs after claiming a dramatic 28-27 injury-time victory over Gloucester at Kingsholm.
Wasps were unable to improve their chances of avoiding relegation from the Premiership on Saturday evening, losing 32-15 against Northampton.
A 10th defeat in 11 games leaves them just eight points above bottom club Newcastle, who lost to Worcester on Friday night, and their showdown at Wasps' ground in the final game of the season could decide who drops into the Championship.
Northampton's sixth win in their last eight games moved them into third place above Leicester, who meet London Irish on Sunday, and while they deserved to win they left it until the 75th minute to score the bonus-point try.
Harlequins regained top spot in the Premiership less than 24 hours after being deposed by reigning champions Saracens.
Their six-month tenure at the head of the table was briefly interrupted when Sarries won 45-9 at Sale on Friday night.
But, in front of a 13,882 sell-out crowd at The Stoop, three penalties from former New Zealand flyhalf Nick Evans and a late try by replacement flank Maurie Fa'asavalu secured a hard-fought victory for the log leaders.
Harlequins 14-6 Bath
Bath took the game to Quins in the first half but a try-saving tackle by Quins fullback Mike Brown, back from Six Nations bench duty with England, kept them out.
After prop David Wilson picked up a loose ball at the breakdown, flank Carl Fearns looked to have put number eight Simon Taylor clear until Brown produced a textbook tackle round the former Scotland star's ankles.
Quins responded with a fast-moving counter-attack involving centre George Lowe and right wing Tom Williams before Brown was forced into touch.
A similar move, instigated by scrumhalf Danny Care, ended with Williams being stopped just short after taking a pass from Brown.
But the home side were temporarily reduced to 14 men when prop Joe Marler was yellow-carded by referee Wayne Barnes for a 30th-minute high tackle on Bath left wing Tom Biggs.
Bath took the lead two minutes later when Quins were caught offside in front of their posts and Heathcote kicked the simple penalty.
Bath began the second half with a flourish. Heathcote split the Quins defence with a darting run and found right wing Olly Woodburn but he was stopped in full flight by former England wing Ugo Monye's excellent tackle. Heathcote put a close-range penalty kick wide and Bath were then denied a try by the television match official.
Fullback Nick Abendanon set up the chance with a piercing run before sidefooting his kick to the corner. It found Woodburn who went over but the replay showed that he had knocked on.
Abendanon then came to Bath's rescue, bravely diving on the ball as three Quins players bore down on him but he was injured in the process and replaced by Jack Cuthbert.
Evans' day went from bad to worse when he spurned a penalty shot at goal and went for touch only to squander the attacking opportunity by kicking the ball beyond the corner flag. The Kiwi flyhalf finally made amends, kicking a 61st-minute penalty from wide on the left to level the scores.
Three minutes later the Quins scrum forced another penalty as they drove Bath back and Evans kicked them ahead from 40 metres.
Bath suffered a further blow when Cuthbert was sin-binned after referee Barnes ruled that he had tackled Brown in the air as the fullback fielded a high kick but it was a desperately close call.
Quins sealed victory in the 74th minute. Brown was tackled just short but replacement scrumhalf Karl Dickson delivered a short pass to send Fa'asavalu crashing over. Evans' conversion attempt rebounded from the post.
Fa'asavalu was yellow-carded two minutes later for a dangerous challenge on Heathcote but Cuthbert hit the post with the resulting penalty and then missed the chance of a losing bonus point for Bath when he was wide again with the last kick of the match.
Pens: Evans 3
Pens: Heathcote 2
Harlequins: 15 Mike Brown, 14 Tom Williams, 13 George Lowe, 12 Jordan Turner-Hall, 11 Ugo Monye, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Luke Wallace, 6 Tom Guest, 5 George Robson (captain), 4 Olly Kohn, 3 James Johnston, 2 Joe Gray, 1 Joe Marler.
Replacements: 16 Rob Buchanan, 17 Mark Lambert, 18 Will Collier, 19 Tomas Vallejos, 20 Maurie Fa'asavalu, 21 Karl Dickson, 22 Rory Clegg, 23 Ross Chisholm.
Bath: 15 Nick Abendanon, 14 Olly Woodburn, 13 Matt Carraro, 12 Olly Barkley, 11 Tom Biggs, 10 Tom Heathcote, 9 Michael Claassens, 8 Simon Taylor, 7 Francois Louw (captain), 6 Carl Fearns, 5 Ryan Caldwell, 4 Dave Attwood, 3 David Wilson, 2 Pieter Dixon, 1 Nathan Catt.
Replacements: 16 Ross Batty, 17 Charlie Beech, 18 Kane Palma-Newport, 19 Ben Skirving, 20 Guy Mercer, 21 Mark McMillan, 22 Dan Hipkiss, 23 Jack Cuthbert.
Referee: Wayne Barnes
Northampton Saints 32-15 London Wasps
Wasps' points all came from the boot of flyhalf Nicky Robinson, who kicked five penalties.
Northampton were without hooker Dylan Hartley and flank Calum Clark, who both face disciplinary hearings next week, but England wing Chris Ashton returned for his first game since January when he had a bust-up with director of rugby Jim Mallinder.
Wasps have had a shocking time with injuries and their curse struck again in the warm-up when replacement Ryan Davies picked up a knock and was replaced by teenager Tom Pridie, who is on loan from Ospreys.
Despite their problems, Wasps made all the running early on, had the edge in the scrum and, but for a forward pass, might have scored through fullback Hugo Southwell.
But their injury jinx struck twice more, centre Dominic Waldouck and flank Jonathan Poff both going off, and they went in at half-time trailing 22-9 having shipped three tries.
Tries: Foden 2, Downey, Roberts
Cons: Lamb 2, Myler
Pens: Lamb 2
Pens: Robinson 5
Northampton: 15 Ben Foden, 14 Chris Ashton, 13 George Pisi, 12 James Downey, 11 Paul Diggin, 10 Ryan Lamb, 9 Lee Dickson (captain), 8 Roger Wilson, 7 Tom Wood, 6 Phil Dowson, 5 Christian Day, 4 James Craig, 3 Brian Mujati, 2 Andy Long, 1 Soane Tonga'uiha.
Replacements: 16 Ross McMillan, 17 Alex Waller, 18 Paul Doran-Jones, 19 Mark Sorenson, 20 Teimana Harrison, 21 Martin Roberts, 22 Stephen Myler, 23 Tom May.
Wasps: 15 Hugo Southwell (captain), 14 Jack Wallace, 13 Elliot Daly, 12 Dom Waldouck, 11 Richard Haughton, 10 Nick Robinson, 9 Nic Berry, 8 Sam Jones, 7 Jonathan Poff, 6 Joe Launchbury, 5 Richard Birkett, 4 James Cannon, 3 Ben Broster, 2 Tom Lindsay, 1 Tim Payne.
Replacements: 16 Vladislav Korshunov, 17 Sakaria Taulafo, 18 Simon McIntyre, 19 Ed O'Donoghue, 20 John Hart, 21 Charlie Davies, 22 Ryan Davis, 23 Paul Emerick.
Referee: Tim Wigglesworth
Exeter Chiefs 28-27 Gloucester
Exeter looked as though would head back down the M5 with only a losing bonus point, secured by Steenson's late penalty, and they would have been kicking themselves after prop Craig Mitchell and wing Matt Jess claimed first-half tries.
Flyhalf Ignacio Mieres added two penalties and a conversion, but just when it looked as though Exeter were finished they dug deep to claim a first win in their history at Kingsholm.
It represented a memorable recovery act - and a considerable show of character - leaving Gloucester to reflect on playing their part in a 55-point thriller, but with nothing to show for it apart from a losing bonus.
Tries: Simpson-Daniel, Burns, Runciman
Cons: Burns 3
Pens: Burns 2
For Exeter Chiefs:
Tries: Mitchell, Jess, Muldowney
Cons: Mieres Steenson
Pens: Mieres 2, Steenson
Gloucester: 15 Jonny May, 14 Charlie Sharples, 13 Mike Tindall, 12 Eliota Fuimaono-Sapolu, 11 James Simpson-Daniel, 10 Freddie Burns, 9 Dave Lewis, 8 Luke Narraway (captain), 7 Akapusi Qera, 6 Matt Cox, 5 Alex Brown, 4 Jim Hamilton, 3 Rupert Harden, 2 Scott Lawson, 1 Dan Murphy.
Replacements: 16 Darren Dawidiuk, 17 Yann Thomas, 18 Dario Chistolini, 19 Tom Savage, 20 Peter Buxton, 21 Nick Runciman, 22 Tim Taylor, 23 Tim Molenaar
Exeter Chiefs: 15 Phil Dollman, 14 Gonzalo Camacho, 13 Bryan Rennie, 12 Jason Shoemark, 11 Matt Jess, 10 Ignacio Mieres, 9 Haydn Thomas, 8 Richard Baxter, 7 James Scaysbrook, 6 Tom Johnson, 5 James Hanks, 4 Tom Hayes (captain), 3 Craig Mitchell, 2 Chris Whitehead, 1 Hoani Tui.
Replacements: 16 Neil Clark, 17 Ben Moon, 18 Chris Budgen, 19 Aly Muldowney, 20 Ben White, 21 Kevin Barrett, 22 Gareth Steenson, 23 Sireli Naqelevuki.
Referee: Greg Garner
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