Gloucester moved two points behind third-placed Harlequins after claiming a 17-15 victory over the Premiership champions at Kingsholm on Friday.
Roared on by the home crowd, Nigel Davies' side drew level on points with fourth-placed Saints, while Quins were left to consider whether their gamble to rest several players was such a wise decision.
Davies made four changes to his Gloucester pack, introducing Koree Britton for his first start of the season at hooker after impressive performances as replacement during the year so far.
Lua Lokotui returned to the second-row, while Tom Savage and Akapusi Qera returned to the back-row. The only change to the Gloucester backline saw Henry Trinder replace Mike Tindall in the midfield.
With only a five day turnaround after the loss at Saracens last week, Conor O'Shea made six changes to his starting line-up. Ross Chisholm, George Lowe and Tom Casson came in to the backline, while up front, Rob Buchanan, Olly Kohn and Luke Wallace joined the pack, with Joe Trayfoot introduced as a late replacement for Tom Guest in the back row to make his first Premiership start.
Gloucester were hampered early on with the loss of captain Jim Hamilton, limping off to be replaced by Will James.
Buchanan earned Quins their first try of the night, charging through the Gloucester defence to score in the corner.
Freddie Burns brought his side back with a penalty goal halfway through the period, before Sam Smith was able to collect Evans' clever chip over the defensive line to race clear and add to Quins' try tally.
The Cherry and Whites failed to reduce the arrears as the break approached, with Burns missing a chance for a second penalty goal in the final minute of the first period.
Charlie Sharples caused panic in the Quins defence, as his run deep into opposition territory led to their first try of the game, with Jonny May eventually flying over the line three minutes after the restart. With Burns converting, the gap was down to two points, and it was game on.
Evans stretched his side's lead with a simple penalty goal after 55 minutes, but Joe Gray was yellow carded with 12 minutes remaining, giving Gloucester the numerical advantage as they sought to overcome the deficit.
Qera took full advantage of the extra man, stretching over the line to draw his side level, and with Burns converting, the Cherry and Whites took the lead for the first time, consigning Harlequins to their third consecutive defeat for the first time in three years.
Tries: May, Qera
Con: Burns 2
Tries: Buchanan, Smith
Gloucester: 15 Rob Cook, 14 Charlie Sharples, 13 Henry Trinder, 12 Billy Twelvetrees, 11 Jonny May, 10 Freddie Burns, 9 Dan Robson, 8 Sione Kalamafoni, 7 Akapusi Qera, 6 Tom Savage, 5 Jim Hamilton (c), 4 Lua Lokotui, 3 Shaun Knight, 2 Koree Britton, 1 Dan Murphy.
Replacements: 16 Huia Edmonds, 17 Nick Wood, 18 Dario Chistolini, 19 Will James, 20 Andy Hazell, 21 Dave Lewis, 22 Mike Tindall, 23 Martyn Thomas.
Harlequins: 15 Mike Brown, 14 Ross Chisholm, 13 George Lowe, 12 Tom Casson, 11 Sam Smith, 10 Nick Evans, 9 Danny Care, 8 Nick Easter (c), 7 Luke Wallace, 6 Tom Guest, 5 George Robson, 4 Olly Kohn, 3 James Johnston, 2 Rob Buchanan, 1 Joe Marler.
Replacements: 16 Joe Gray, 17 Mark Lambert, 18 Will Collier, 19 Charlie Matthews, 20 Joe Trayfoot, 21 Karl Dickson, 22 Ben Botica, 23 Matt Hopper.
Referee: JP Doyle
Assistant referees: Kevin Stewart, Stuart Terheege
TMO: Geoffrey Warren